upload: Return correct tuple values in _ProcessResults

Incorrect tuple values were returned with http://go/grev/440221 -
instead of returning (Project, ReviewableBranch), _ProcessResults was
returning (int, ReviewableBranch).

R=jojwang@google.com

Bug: 376731172
Change-Id: I75205f42fd23f5ee6bd8d0c15b18066189b42bd9
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/441121


Reviewed-by: Sam Saccone <samccone@google.com>
Commit-Queue: Josip Sokcevic <sokcevic@google.com>
Tested-by: Josip Sokcevic <sokcevic@google.com>