Avoid taking GitHub fast path for git clones

[ibraheemdev]

Avoid using github_fast_path for the initial clone of a repository. This would require using git clone instead of git init + git fetch, and using the --branch argument to resolve refspecs.

[charliermarsh]

What's the motivation?

[samypr100]

There were also some discussions about other approaches in #3287

[ibraheemdev]

That discussion is mostly unrelated to this. The GitHub fast path primarily tells us if the commit we have is up to date, so we shouldn't need to take it for the initial clone.

[charliermarsh]

Don't we need to figure out the precise commit from (e.g.) the branch / tag though? I thought we skipped this anyway if we had a precise commit already, and that the fast path was mostly for that operation.

[ibraheemdev]

I don't see an early return in github_fast_path unless we find the local repo is up to date, and the resulting oid is used pretty rarely.