Tests in Github and Gitlab integrations should actually clone a repo

[WWM-jschuba]

Describe the current behavior

Currently, the tests for prefect-github and prefect-github get_directory() function only test part of the functionality. They do not actually clone a repo, which is the major purpose of that function.

The tests mock up a temp directory, with files inside. Because that directory is not empty, the git clone command silently fails. The remainder of the function successfully copies the pre-made files, and returns a full destination directory.

This appears to be the intention of the test writer. The test might be slow if it actually cloned a git repo, however, that critical component remains untested.

As a result, several bugs made it into production. Some examples:
#11279
#13180
#15206
#15236

Describe the proposed behavior

Create new tests in prefect-github and prefect-gitlab that clone a repo, and verify that it was cloned successfully. Example is below.

We need to decide what repo to clone. The prefect repo is quite large. We might also want to test the cloning of a private repo with secret keys.

async def test_get_directory_clones_a_repo(self, monkeypatch):  # noqa
        """Check that `get_directory` is able to clone a repo"""  # noqa

        with TemporaryDirectory() as tmp_dst:

            g = GitHubRepository(
                repository_url="https://github.com/PrefectHQ/prefect.git",
            )
            await g.get_directory(local_path=tmp_dst)

            # Verify that we cloned the repo
            dir_list = set(os.listdir(tmp_dst))
            assert 'README.md' in dir_list  # The repo should have a README at the root
            assert '.git' in dir_list  # The repo should have a .git directory

Example Use

N/A. This is a proposal for new tests.

Additional context

No response