packit: use the closest matching tag for the checked out revision

packit: use the closest matching tag for the checked out revision

Packit otherwise tries to get the latest tag by creation date, which
doesn't work well in the systemd-stable repo:

2024-01-23 13:40:47.858 upstream.py       DEBUG  No ref given or is not glob pattern
2024-01-23 13:40:47.859 upstream.py       DEBUG  We're about to get latest matching tag in the upstream repository /tmp/tmp07g2beo8.
2024-01-23 13:40:47.859 commands.py       DEBUG  Command: git tag --list --sort=-creatordate
2024-01-23 13:40:47.866 logging.py        DEBUG  v248.13
2024-01-23 13:40:47.866 logging.py        DEBUG  v249.17
2024-01-23 13:40:47.866 logging.py        DEBUG  v250.14
2024-01-23 13:40:47.866 logging.py        DEBUG  v251.20
2024-01-23 13:40:47.867 logging.py        DEBUG  v252.21
2024-01-23 13:40:47.867 logging.py        DEBUG  v253.15
2024-01-23 13:40:47.867 logging.py        DEBUG  v254.8
2024-01-23 13:40:47.867 logging.py        DEBUG  v255.2
2024-01-23 13:40:47.868 logging.py        DEBUG  v255.1
2024-01-23 13:40:47.868 logging.py        DEBUG  v255
...