Is your feature request related to a problem? Please describe.
Currently git 2.40 has some buggy behaviour that emerges with rust, see arxanas/git-branchless#894 and libgit2/libgit2#6531

Describe the solution you'd like
Allowing git to be not managed by fleek -- this is a bit of a toe stubber and being able to have a system git used would be nice

Describe alternatives you've considered
Having git version be able to be tightly controlled by fleek e.g, being able to rollback to git 2.39.2 would work, however this doesn't seem to be a natural use case of nix