Optimize code owners file section regex
What does this MR do and why?
We require a section at the beginning of the line. If it doesn't exist there, there's no need to search for it there. Since it doesn't cause a high load spike, then we can fix it as a performance issue: https://gitlab.com/gitlab-org/gitlab/-/issues/385883#note_1210910052
Edited by Igor Drozdov