In commit 0a90028f (checks: Speed up retrieving commits via
quarantine directory, 2021-07-29), the Gitlab::Git::Repository class got
a new optional parameter `allow_quarnatine` for `#new_commits()`. The
commit forgot to amend the Repository model though to accept the same
parameter, which as a result leads to a runtime error when the access
checks try to load new commits.

Fix this issue by adding the missing parameter to the Repository model.
This commit also changes the changes access spec to call the original
function such that the bug would've been caught without the fix.

Changelog: fixed