refs/heads/master cannot be updated to an annotated tag per se; the rev
given must first be resolved to a commit. ^{commit} recursively
dereferences the rev until a commit is found.
Resolves#6737 and test failure:
# bats --filter annotated-tag tests/unit/git_3.bats
git_3.bats
✗ (git) git:sync existing [--no-build annotated-tag]
fatal: update_ref failed for ref 'refs/heads/master': cannot update ref 'refs/heads/master': trying to write non-commit object 6399bed673f513332f3d5d99e777e0262f42404c to branch 'refs/heads/master'
f64cf3bdfa