Make the "git" cargo module optional for releases

[cryptomilk]

Describe the bug

It looks like there is a dependency on the git library to get better version information. This should only be required for nightly builds but not for releases.

[lu-zero]

git2 is a dependency coming from https://crates.io/crates/built, if you open a pr to forward the feature selection and I'd land it immediately.

[LigH-de]

Possible regression? Building in MSYS2/MinGW failed today. GCC was updated to 14.1 recently.

[lu-zero]

How does it break?

[LigH-de]

m-ab-s/media-autobuild_suite#2670

logs.zip (collected by M-AB-S) contains a lot of possibly relevant log files

  = note: G:/MABS/msys64/mingw32/bin/../lib/gcc/i686-w64-mingw32/14.1.0/../../../../i686-w64-mingw32/bin/ld.exe: cannot find -lgit2: No such file or directory
          collect2.exe: error: ld returned 1 exit status
          

error: could not compile `rav1e` (build script) due to 1 previous error
warning: build failed, waiting for other jobs to finish...
Error: CliError { error: Some(1 job failed), exit_code: 101 }

[LigH-de]

In case it matters: G:\MABS\build\rav1e-git\target\release-no-lto\build\libgit2-sys-c7fedf06edef2971\out\build\libgit2.a does exist. I am not surprised that ld can't find it there.
Apart from that, I am no developer, I don't know which files ld might be looking for at all. For libraries to be linked static, I only ever knew *.a files.

[lu-zero]

built seems to unconditionally bring in git2.