Update accept header used with GraphQL17Alpha9Handler (#12973)

Updates the header based on changes in apollographql/apollo-server#8148

Author: jerelmiller

.changeset/slimy-ducks-scream.md

@@ -0,0 +1,5 @@
+---
+"@apollo/client": patch
+---
+
+Update the `accept` header used with the `GraphQL17Alpha9Handler` to `multipart/mixed;incrementalSpec=v0.2` to ensure the newest incremental delivery format is requested.

.size-limits.json

@@ -1,6 +1,6 @@
 {
-  "import { ApolloClient, InMemoryCache, HttpLink } from \"@apollo/client\" (CJS)": 44752,
-  "import { ApolloClient, InMemoryCache, HttpLink } from \"@apollo/client\" (production) (CJS)": 39500,
-  "import { ApolloClient, InMemoryCache, HttpLink } from \"@apollo/client\"": 33897,
-  "import { ApolloClient, InMemoryCache, HttpLink } from \"@apollo/client\" (production)": 27749
+  "import { ApolloClient, InMemoryCache, HttpLink } from \"@apollo/client\" (CJS)": 44831,
+  "import { ApolloClient, InMemoryCache, HttpLink } from \"@apollo/client\" (production) (CJS)": 39452,
+  "import { ApolloClient, InMemoryCache, HttpLink } from \"@apollo/client\"": 33875,
+  "import { ApolloClient, InMemoryCache, HttpLink } from \"@apollo/client\" (production)": 27756
 }

src/incremental/handlers/graphql17Alpha9.ts

@@ -259,7 +259,11 @@ export class GraphQL17Alpha9Handler
     if (hasDirectives(["defer", "stream"], request.query)) {
       const context = request.context ?? {};
       const http = (context.http ??= {});
-      http.accept = ["multipart/mixed", ...(http.accept || [])];
+      // https://specs.apollo.dev/incremental/v0.2/
+      http.accept = [
+        "multipart/mixed;incrementalSpec=v0.2",
+        ...(http.accept || []),
+      ];
 
       request.context = context;
     }

src/link/http/__tests__/HttpLink.ts

@@ -1636,7 +1636,7 @@ describe("HttpLink", () => {
             headers: {
               "content-type": "application/json",
               accept:
-                "multipart/mixed,application/graphql-response+json,application/json;q=0.9",
+                "multipart/mixed;incrementalSpec=v0.2,application/graphql-response+json,application/json;q=0.9",
             },
           })
         );
@@ -1744,7 +1744,7 @@ describe("HttpLink", () => {
             headers: {
               "content-type": "application/json",
               accept:
-                "multipart/mixed,application/graphql-response+json,application/json;q=0.9",
+                "multipart/mixed;incrementalSpec=v0.2,application/graphql-response+json,application/json;q=0.9",
             },
           })
         );