Update pull mirroring test to use admin creds
What does this MR do?
Updates the test to use admin credentials as a workaround for a permissions bug. See #13769 (closed)
Ideally, we wouldn't use admin credentials for this test because it shouldn't need them. But this lets us keep the test running. When #13769 (closed) is fixed we can switch back to the default credentials.
Closes #33759 (closed)