Empty artifacts after the libgit2 upgrade to 1.3.0

[stefanprodan]

After upgrading my cluster to the latest build from main ghcr.io/fluxcd/source-controller:rc-b65cf9d5, using gitImplementation: libgit2 with both https and ssh result in empty artifacts. I think this bug was introduced in #573

[hiddeco]

Above issue is just for branches, and also the single test scenario in which we lacked a confirmation on Artifact size.

[hiddeco]

After cloning and checking out the Git repository, something seems to alter the state of the folder on the FS, making Git itself think that files have been removed:

$ cd /tmp/test3946352686
$ git status
On branch master
Your branch is up to date with 'origin/master'.

Changes to be committed:
  (use "git restore --staged <file>..." to unstage)
        deleted:    branch

If you explicitly check out the resolved HEAD reference using checkoutDetachedHEAD (as used by others) in CheckoutBranch#Checkout, this seems to revert the changes:

...
	cc, err := repo.LookupCommit(head.Target())
	if err != nil {
		return nil, fmt.Errorf("could not find commit '%s' in branch '%s': %w", head.Target(), c.Branch, err)
	}
	defer cc.Free()
	ccc, err := checkoutDetachedHEAD(repo, cc.Id())
	if err != nil {
		return nil, fmt.Errorf("failed to checkout head")
	}
	return buildCommit(ccc, "refs/heads/"+c.Branch), nil

This gives me gut feeling that the the CheckoutBranch flag from CloneOptions either broke, or changed behavior.