fix(batches): don't request unnecessary info that's likely to cause GH errors (#64299)

Closes SRCH-802

After a long and unsuccessful hunt of eventual consistency errors, I
noticed that we don't need the GraphQL fragments that are causing
problems.

I introduced a simplified request, which succeeds reliably. What
customers should see now is one error (see second picture below), which
is followed by a retry, and then success.

Previously we've seen this error, sometimes less often, sometimes more,
but customers saw it so often that it caused their batch changes to
fail.

<img width="1042" alt="Screenshot 2024-08-06 at 14 02 00"
src="https://github.com/user-attachments/assets/c5a099da-d474-43db-ac12-ac7c4f22d4d3">

Customers may still see an initial error, which I've seen to reliably
disappear on the first retry. It should not be a problem

<img width="1039" alt="Screenshot 2024-08-06 at 14 02 48"
src="https://github.com/user-attachments/assets/99f278d4-4020-48ea-b4ac-32cbdfce455d">

## Test plan

Manual testing

## Changelog

- fix(batches): improve GitHub Apps integration reliability by
simplifying the data requested from GitHub

Author: bahrmichael

internal/batches/sources/github.go

@@ -231,7 +231,7 @@ func (s GitHubSource) createChangeset(ctx context.Context, c *Changeset, prInput
 		if err != nil {
 			return exists, errors.Wrap(err, "getting repo owner and name")
 		}
-		pr, err = s.client.GetOpenPullRequestByRefs(ctx, owner, name, c.BaseRef, c.HeadRef)
+		pr, err = s.client.GetOpenPullRequestByRefsReduced(ctx, owner, name, c.BaseRef, c.HeadRef)
 		if err != nil {
 			return exists, errors.Wrap(err, "fetching existing PR")
 		}

internal/batches/sources/testdata/golden/GithubSource_CreateChangeset_already_exists

@@ -11,141 +11,33 @@
   "Number": 1,
   "ReviewDecision": "REVIEW_REQUIRED",
   "Author": {
-   "AvatarURL": "https://avatars.githubusercontent.com/u/1185253?u=35f048c505007991433b46c9c0616ccbcfbd4bff\u0026v=4",
-   "Login": "mrnugget",
-   "URL": "https://github.com/mrnugget"
-  },
-  "BaseRepository": {
-   "ID": "MDEwOlJlcG9zaXRvcnkyMjExNDc1MTM=",
-   "Name": "automation-testing",
-   "Owner": {
-    "Login": "sourcegraph"
-   }
-  },
-  "HeadRepository": {
-   "ID": "MDEwOlJlcG9zaXRvcnkyMjExNDc1MTM=",
-   "Name": "automation-testing",
-   "Owner": {
-    "Login": "sourcegraph"
-   }
-  },
-  "Participants": [
-   {
-    "AvatarURL": "https://avatars.githubusercontent.com/u/1185253?u=35f048c505007991433b46c9c0616ccbcfbd4bff\u0026v=4",
+    "AvatarURL": "https://avatars3.githubusercontent.com/u/1185253?v=4",
     "Login": "mrnugget",
     "URL": "https://github.com/mrnugget"
-   },
-   {
-    "AvatarURL": "https://avatars.githubusercontent.com/u/19534377?v=4",
-    "Login": "eseliger",
-    "URL": "https://github.com/eseliger"
-   }
-  ],
-  "Labels": {
-   "Nodes": []
   },
-  "TimelineItems": [
-   {
-    "Type": "PullRequestCommit",
-    "Item": {
-     "Commit": {
-      "OID": "9d04a0d8733dafbb5d75e594a9ec525c49dfc975",
-      "Message": "Add another file",
-      "MessageHeadline": "Add another file",
-      "URL": "https://github.com/sourcegraph/automation-testing/commit/9d04a0d8733dafbb5d75e594a9ec525c49dfc975",
-      "Committer": {
-       "AvatarURL": "https://avatars.githubusercontent.com/u/1185253?v=4",
-       "Email": "[email protected]",
-       "Name": "Thorsten Ball",
-       "User": {
-        "AvatarURL": "https://avatars.githubusercontent.com/u/1185253?u=35f048c505007991433b46c9c0616ccbcfbd4bff\u0026v=4",
-        "Login": "mrnugget",
-        "URL": "https://github.com/mrnugget"
-       }
-      },
-      "CommittedDate": "2019-11-12T06:38:55Z",
-      "PushedDate": "2019-11-12T06:39:00Z"
-     }
-    }
-   },
-   {
-    "Type": "PullRequestCommit",
-    "Item": {
-     "Commit": {
-      "OID": "37406e7dfa4466b80d1da183d6477aac16b1e58c",
-      "Message": "Test commit to always have a open PR",
-      "MessageHeadline": "Test commit to always have a open PR",
-      "URL": "https://github.com/sourcegraph/automation-testing/commit/37406e7dfa4466b80d1da183d6477aac16b1e58c",
-      "Committer": {
-       "AvatarURL": "https://avatars.githubusercontent.com/u/1185253?v=4",
-       "Email": "[email protected]",
-       "Name": "Thorsten Ball",
-       "User": {
-        "AvatarURL": "https://avatars.githubusercontent.com/u/1185253?u=35f048c505007991433b46c9c0616ccbcfbd4bff\u0026v=4",
-        "Login": "mrnugget",
-        "URL": "https://github.com/mrnugget"
-       }
-      },
-      "CommittedDate": "2019-11-12T06:39:23Z",
-      "PushedDate": "2019-11-12T06:39:33Z"
-     }
-    }
-   },
-   {
-    "Type": "ClosedEvent",
-    "Item": {
-     "Actor": {
-      "AvatarURL": "https://avatars.githubusercontent.com/u/19534377?v=4",
-      "Login": "eseliger",
-      "URL": "https://github.com/eseliger"
-     },
-     "CreatedAt": "2019-12-04T23:28:16Z",
-     "URL": "https://github.com/sourcegraph/automation-testing/pull/1#event-2855920542"
-    }
-   },
-   {
-    "Type": "ReopenedEvent",
-    "Item": {
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-      "Login": "mrnugget",
-      "URL": "https://github.com/mrnugget"
-     },
-     "CreatedAt": "2019-12-05T07:09:21Z"
+  "BaseRepository": {
+    "ID": "MDEwOlJlcG9zaXRvcnkyMjExNDc1MTM=",
+    "Name": "automation-testing",
+    "Owner": {
+      "Login": "sourcegraph"
     }
-   },
-   {
-    "Type": "RenamedTitleEvent",
-    "Item": {
-     "Actor": {
-      "AvatarURL": "https://avatars.githubusercontent.com/u/1185253?u=35f048c505007991433b46c9c0616ccbcfbd4bff\u0026v=4",
-      "Login": "mrnugget",
-      "URL": "https://github.com/mrnugget"
-     },
-     "PreviousTitle": "This is a test PR that is always open",
-     "CurrentTitle": "This is a test PR that is always open (keep it open!)",
-     "CreatedAt": "2019-12-05T07:09:31Z"
+  },
+  "HeadRepository": {
+    "ID": "MDEwOlJlcG9zaXRvcnkyMjExNDc1MTM=",
+    "Name": "automation-testing",
+    "Owner": {
+      "Login": "sourcegraph"
     }
-   }
-  ],
+  },
   "Commits": {
-   "Nodes": [
-    {
-     "Commit": {
-      "OID": "37406e7dfa4466b80d1da183d6477aac16b1e58c",
-      "CheckSuites": {
-       "Nodes": []
-      },
-      "Status": {
-       "State": "",
-       "Contexts": null
-      },
-      "CommittedDate": "2019-11-12T06:39:23Z"
-     }
-    }
-   ]
+    "Nodes": []
+  },
+  "Labels": {
+    "Nodes": []
   },
+  "Participants": [],
+  "TimelineItems": [],
   "IsDraft": false,
   "CreatedAt": "2019-11-12T06:40:21Z",
   "UpdatedAt": "2023-02-03T20:42:20Z"
- }
+}