fix(ci): split up checkout steps for push vs. pull request (#3911)

.github/workflows/javascript-tests.yml

@@ -17,8 +17,15 @@ jobs:
         with:
           concurrent_skipping: 'same_content_newer'
 
-      - name: Checkout
+      - name: Check out pull request code
         uses: actions/checkout@v4
+        if: github.event_name == 'pull_request'
+        with:
+          repository: ${{ github.event.pull_request.head.repo.full_name }}
+
+      - name: Check out repository code
+        uses: actions/checkout@v4
+        if: github.event_name == 'push'
 
       - uses: actions/setup-node@v4
         with: