[gitlab-org/gitlab] Merge requests do not update after upgrading to CE-18.9.1

### ROOT CAUSE The issue is caused by a regression in the `UpdateMergeRequestsWorker` job introduced in GitLab CE 18.9.1. The worker attempts to update the `merge_request_diff_commits` table with a `null` value for the `committed_date` column, violating its `NOT NULL` constraint. This behavior is triggered by merge request diff commits during the upgrade process. ### CODE FIX 1. **Revert the Worker's Behavior**: Modify the `UpdateMergeRequestsWorker` to handle cases where `diff_commits` might not have a `committed_date`. Specifically, avoid setting `null` for this column. ```ruby:app/workers/update_merge_requests_worker.rb # In the method that updates the diff_commits if diff_commits # Only update the committed_date if it exists, else skip next unless diff_commits.committed_date # Your existing code to update the date end ``` 2. **Ensure Proper Data Migration**: If the `UpdateMergeRequestsWorker` is part of a larger upgrade process, ensure any associated data migrations (e.g., `20230101000000`) properly handle the `merge_request_diff_commits` table. **Steps to Apply the Fix**: 1. Replace the existing code in `UpdateMergeRequestsWorker` with the above conditional check. 2. Run the Sidekiq jobs again to process pending merge requests. 3. Verify that the `merge_request_diff_commits` table no longer contains `null` values for `committed_date`. This fix ensures the database constraint is respected and allows merge requests to update properly post-upgrade.