run-tests: Use git protocol.file.allow

git v2.38.1 changed its behavior to not allow this by default due to security issues:

https://vielmetti.typepad.com/logbook/2022/10/git-security-fixes-lead-to-fatal-transport-file-not-allowed-error-in-ci-systems-cve-2022-39253.html

Should not be a problem as the git repos are created in during the test.