fix(ci): skip release-draft update on pull_request events

Release Drafter fails on every PR with "Validation Failed: target_commitish"
because it tries to use refs/pull/NNN/merge as the release target. Gate the
update_release_draft job with `if: github.event_name == 'push'` so it only runs
on pushes to the default branch, while keeping the pull_request trigger so the
autolabeler can be enabled later.

Cherry-picks only the workflow fix from #161 (which was based on a stale main
and carried unrelated changes).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: 2 people

.github/workflows/release-drafter.yml

@@ -25,6 +25,10 @@ jobs:
       # otherwise, read permission is required at least
       pull-requests: write
     runs-on: ubuntu-latest
+    # Only update the release draft on push to main, not on pull_request events.
+    # Running on PRs causes "Validation Failed: target_commitish" because
+    # release-drafter tries to set refs/pull/NNN/merge as the release target.
+    if: github.event_name == 'push'
     steps:
       # (Optional) GitHub Enterprise requires GHE_HOST variable set
       #- name: Set GHE_HOST