Use same regex expression to match stable branches

There is a subtle difference in using non-capturing
groups. Even though both regex expressions result in
a match, the one with the non-capturing group won't
let us know the branch and it's not consistent with
the other regex expressions in this file.

Change-Id: I1062ef7b19dc27b93ce52abebe83847b4bd3f172
Merge "Use same regex expression to match stable branches"