Use bounded git rev-list for version detection

[pavelToman]

This PR avoids an unnecessary full Git history traversal during EasyBuild version detection.

Currently the code uses git rev-list HEAD and then only keeps the first returned commit hash. On large repositories or filesystems with slow metadata access, this can make even simple commands like eb --version noticeably slow, because git rev-list HEAD walks the full reachable commit history.

Since EasyBuild only needs the current HEAD commit hash here, this PR changes the call to the equivalent of:

git rev-list -n 1 HEAD

This preserves the existing GitPython-based implementation and the resulting version string, but avoids traversing more history than needed.

In my local testing on an HPC filesystem, this reduced warm eb --version startup time from many seconds to about 0.5 s, while keeping the same reported EasyBuild version and Git revision hashes.
This is the matching change for the same version-detection pattern in easyblocks.

*this PR was created with help of ChatGPT5.5

Framework PR:

• Use bounded git rev-list for version detection easybuild-framework#5201