Merge branch 'cc/tests-without-assuming-ref-files-backend'

Quite a many tests assumed that newly created refs are made as loose refs using the files backend, which have been updated to use proper plumbing like rev-parse and update-ref, to avoid breakage once we start using different ref backends. * cc/tests-without-assuming-ref-files-backend: t990X: use '.git/objects' as 'deep inside .git' path t: make many tests depend less on the refs being files