Revert "Merge branch 'pks-ci-use-gitaly-git' into 'master'"

What does this MR do and why?

This reverts !72366 (merged) because the bump in the required Git version is not playing well with CI at the moment.

We've got a chicken and egg problem in https://gitlab.com/gitlab-org/gitlab/-/jobs/1704115864#L65. setup-test-env fails because gitaly-test-build doesn't build Gitaly because the dir is restored from cache, but we need it to regenerate.

Also, setup-test-env fails in master because Gitaly wants Git v2.33, not v2.31.

But then we can't force it to rebuild in !72823 (closed) because tmp/tests/gitaly doesn't actually have all the source files, like go.mod and go.sum.