Determine Icinga 2 git version more reliably

[yhabteab]

fixes #10016

Before:

(venv) ~/Workspace/icinga2 (master ✗) prefix/sbin/icinga2 --version
icinga2 - The Icinga 2 network monitoring daemon (version: v2.14.0-146-g9e31b8b55; debug)

Copyright (c) 2012-2024 Icinga GmbH (https://icinga.com/)
License GPLv2+: GNU GPL version 2 or later <https://gnu.org/licenses/gpl2.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.
...

After:

(venv) ~/Workspace/icinga2 (determine-git-version-for-master ✗) prefix/sbin/icinga2 --version
icinga2 - The Icinga 2 network monitoring daemon (version: v2.14.2-147-ga34eecd85; debug)

Copyright (c) 2012-2024 Icinga GmbH (https://icinga.com/)
License GPLv2+: GNU GPL version 2 or later <https://gnu.org/licenses/gpl2.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.
...