Reduce idle in transaction time when updating a merge request
MergeRequestDiff#save_git_content
can take a while to compute and save
the diffs, and it can hold a transaction in idle for a long time when
it attempts to update the latest latest_merge_request_diff_id
.
To prevent this, we first generate the diff and only after this completes do we update the diff ID.
Closes #33650 (closed)
Edited by Stan Hu