Re-enable git protocol v2 end-to-end tests

Now that git protocol v2 support is re-enabled, we can re-enable the relevant end-to-end tests.

• Update code that was broken while the test wasn't running gitlab-org/gitlab!25496 (merged)
• Wait for gitlab-shell to be updated: gitlab-org/gitlab-shell#273 (closed) and be deployed to staging gitlab-org/gitlab!26256 (merged)
• Re-enable git protocol v2 testing in nightly pipeline config https://gitlab.com/gitlab-org/quality/nightly/-/merge_requests/52
• Re-enable git protocol v2 testing in gitlab-qa pipeline config gitlab-org/gitlab-qa!395 (merged)
• Run the tests against Staging several times to confirm that they pass (they weren't running on Canary and Prod because they're not smoke tests)
• Monitor the nightly runs for a week to confirm that the tests aren't flaky
• Remove the tests from quarantine.