mktag tests: test hash-object --literally and unreachable fsck

mktag tests: test hash-object --literally and unreachable fsck

Extend the mktag tests to pass the tag we've created through both
hash-object --literally and fsck.

This checks that fsck itself will not complain about certain invalid
content if a reachable tip isn't involved. Due to how fsck works and
walks the graph the failure will be different if the object is
reachable, so we might succeed before we've created the ref.

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>