Add git version if running an unreleased version

[sidt4]

From https://appstream.debian.org/logs/2023/10/02_0810.log

2023-10-02 08:10:02 - INFO: AppStream Generator 0.9.1, AS: 0.16.2 [Debian]
2023-10-02 08:10:02 - INFO: Scanning new packages for experimental/main [amd64]

It appears that Debian runs an unreleased ( 0.9.1 ) version for generating appstream. In such cases, it would be useful to print the exact git version along with the AS version, as it would be useful for debugging purposes.

Example:

2023-10-02 08:10:02 - INFO: AppStream Generator 0.9.0 (+git-041fb04), AS: 0.16.2 [Debian]
2023-10-02 08:10:02 - INFO: Scanning new packages for experimental/main [amd64]

2023_10_02_0810.log