tests: promote with simple char escape check

Author: yasunariw

mock_payloads/pull_request_review_comment.created.json

@@ -31,7 +31,7 @@
       "type": "User",
       "site_admin": false
     },
-    "body": "PR review comment example",
+    "body": "PR review comment example with <escaped & characters>",
     "created_at": "2020-05-25T07:37:52Z",
     "updated_at": "2020-05-25T07:38:26Z",
     "html_url": "https://github.com/xinyuluo/pr_test/pull/4#discussion_r429778584",

test/slack_payloads.expected

@@ -403,7 +403,8 @@ will notify #aa-git
       "color": "#ccc",
       "pretext":
         "<https://github.com/xinyuluo/pr_test|[xinyuluo/pr_test]> *xinyuluo* commented on #4 <https://github.com/xinyuluo/pr_test/pull/4|README update>",
-      "text": "PR review comment example",
+      "text":
+        "PR review comment example with &lt;escaped &amp; characters&gt;",
       "footer":
         "New comment by xinyuluo in <https://github.com/xinyuluo/pr_test/pull/4#discussion_r429778584|README.md>"
     }
@@ -419,7 +420,8 @@ will notify #backend
       "color": "#ccc",
       "pretext":
         "<https://github.com/xinyuluo/pr_test|[xinyuluo/pr_test]> *xinyuluo* commented on #4 <https://github.com/xinyuluo/pr_test/pull/4|README update>",
-      "text": "PR review comment example",
+      "text":
+        "PR review comment example with &lt;escaped &amp; characters&gt;",
       "footer":
         "New comment by xinyuluo in <https://github.com/xinyuluo/pr_test/pull/4#discussion_r429778584|README.md>"
     }