Drop minimum required Git version to v2.24.0 again
What does this MR do?
In !38152 (merged), the minimum required version of Git was raised to v2.28.0. Due to a regression in that version (#233964 (closed)), we're deferring the mandatory upgrade until git-core v2.28.1 has been released with a fix to the issue. The regression cannot be hit anymore in Gitaly as the offending hook has been removed in gitaly!2454 (merged), but as this new hook was the main reason why we wanted to push for v2.28.0 it doesn't make sense anymore to make that version mandatory.
So this MR reverts the mandatory requirement, but instead makes it the recommended version. The initial regression would be catched early now as a testcase has been added via gitlab-org/quality/testcases#962 (closed) that makes sure we don't hit it again. Because of this, upgrades of our infra to v2.28.0 are not reverted.