Resolve "Bug: Show an error when using the /merge quick action with an out of date head sha"
requested to merge 355567-bug-show-an-error-when-using-the-merge-quick-action-with-an-out-of-date-head-sha into master
What does this MR do and why?
We do a check in the merge service (https://gitlab.com/gitlab-org/gitlab/-/blob/d14b5c3f85e8c88565c5ad8d6e1bf182a29f7105/app/services/merge_requests/merge_service.rb#L155) to see if the sources matches while locking. But we should also do another check earlier in the process without locking to eliminate the majority of cases where this may occur and return a more appropriate error.
Related to #355567 (closed)
Edited by Marc Shaw