ci(changelog): Only run changelog check in PR (#4851)

The merge group does not have the pull request context, for now skip the
check, until we have a better solution to check changelogs in the merge
queue.

Author: Dav1dde

.github/workflows/changelog.yml

@@ -15,5 +15,7 @@ jobs:
           GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
         with:
           script: |
-            const changelog = require('./.github/actions/changelog/index.js')
-            await changelog({github, context, core})
+            if (context.payload.pull_request) {
+              const changelog = require('./.github/actions/changelog/index.js')
+              await changelog({github, context, core})
+            }