git: Bump minimum required Git version to v2.38.0
Git v2.38.0 brings some important changes with it that we want to build on:
- It fixes a source of corruption when upgrading commit-graphs that
contain generation data in v1 to v2. We currently had to disable
use of generation data completely because of that bug so that we
don't corrupt repositories. This information is important though
to speed up some computations, like for example in the packfile
negotiation.
- git-merge-tree(1) learned two merge two trees. This is important
to allow us to do in-memory merges.
- git-cat-file(1) starts to support mailmaps, which is important for
us to support them in Gitaly.
- git-clone(1) has clearned about bundle URIs, which allows
offloading parts of a clone to a CDN.
Bump the minimum required Git version to v2.38.0.
Closes #4672 (closed).