Do not change in case of manifest sync

In case of manifest/smart sync repo changes ".merge" config
option from branch to SHA. Doing 'repo upload' fails as
repo tries to upload to a remote branch that looks like SHA
(e.g. refs/for/23423423423423423423423)

Do not update the .merge in case if revision is SHA.

Change-Id: I9139708fa17f21eec5a7e23c3255333626bf529e
1 file changed