ci: trigger CI on merge_group so the merge queue can complete

The repository's default-branch ruleset requires the GitHub Merge
Queue, and requires this workflow's Integration and Protocol test
jobs as status checks. The queue runs checks against temporary
gh-readonly-queue/main/* branches, which only trigger workflows that
opt in via the merge_group event. This workflow only had push and
pull_request triggers, so no run ever started for queued entries —
they sat in AWAITING_CHECKS indefinitely, waiting on required checks
that could never execute.

Also extend test-integration-cloud-serverless's forked-PR guard to
allow merge_group events. Without this, adding the trigger above
would make the job run but immediately evaluate its `if` to false and
report skipped — still leaving one of the three required checks
permanently unsatisfied on queue runs.

Author: jstirnaman

.github/workflows/ci.yml

@@ -5,6 +5,7 @@ on:
     branches: [main]
   pull_request:
     branches: [main]
+  merge_group:
   workflow_dispatch:
 
 jobs:
@@ -123,9 +124,12 @@ jobs:
     runs-on: ubuntu-latest
     # Skip on forked PRs — environment secrets (INFLUXDB_CLOUD_URL/TOKEN) are
     # not exposed to fork runs, which would fail on empty credentials.
+    # merge_group runs only happen for same-repo branches that already
+    # cleared review, so they're always safe to include here.
     if: |
       github.repository_owner == 'influxdata' &&
       (github.event_name == 'push' ||
+       github.event_name == 'merge_group' ||
        github.event.pull_request.head.repo.full_name == github.repository)
     environment: cloud-serverless
     steps: