Fix AuthServiceTest for multi-user systems

The test previously assumed a user 0 system. If the tests were run when
the current user is not user 0, they would fail with a
SecurityException. By using the current userId, they will run more
reliably.

Bug: 360942456
Test: atest com.android.server.biometrics.AuthServiceTest
Flag: TEST_ONLY
Change-Id: I9dc8cdfd9cc348e39575777cc069b9a8ba0689a9