Strangely #19038 appears to relate to an issue whereby a tag appears to
be listed in `git show-ref --tags` but then does not appear when `git
show-ref --tags -- short_name` is called.
As a solution though I propose to stop the second call as it is
unnecessary and only likely to cause problems.
I've also noticed that the tags calls are wildly inefficient and aren't using the common cat-files - so these have been added.
I've also noticed that the git commit-graph is not being written on mirroring - so I've also added writing this to the migration which should improve mirror rendering somewhat.
Fix#19038
Signed-off-by: Andrew Thornton <art27@cantab.net>
Co-authored-by: 6543 <6543@obermui.de>
889a8c268c