For groups in NoteDb, we manage group ownership through permissions on
the group ref. During the migration, we prevent the mutation of
Gerrit-managed permissions for group refs to ensure the ReviewDb and
NoteDb data does not get out of sync.
This commit prevents the mutation of access sections through direct Git
pushes.
Change-Id: I9923c003a57fc16de85b91f96901c0e1b398eabc
22f6c58aa0