Ignore merge commits on final release branch check (datacommonsorg#4765)

The final check looks at the branch after merge, which includes merge
commits added by GitHub when merging PRs. These are the only merge
commits that should be allowed in the final release branch commit
history.

.github/workflows/release-branch-checks.yml

@@ -25,8 +25,15 @@ jobs:
           git fetch dc
           MASTER_BRANCH="dc/master"
 
-          # Get the list of commits in the source branch that are not in the master branch
-          MISSING_COMMITS=$(git log --pretty="%H - %s" $MASTER_BRANCH..HEAD --)
+          # Get the list of commits in the source branch that are not in the master branch.
+          # Exclude merge commits only if this is the final run in the merge queue.
+          # This way the only merge commits that end up in the final commit history
+          # are the ones added by GitHub when merging PRs.
+          if [[ ${{ github.event_name }}  == 'merge_group' ]]; then
+            MISSING_COMMITS=$(git log --pretty="%H - %s" --no-merges $MASTER_BRANCH..HEAD --)
+          else
+            MISSING_COMMITS=$(git log --pretty="%H - %s" $MASTER_BRANCH..HEAD --)
+          fi
 
           if [[ -n "$MISSING_COMMITS" ]]; then
             echo ""