Fix testGetProfileIdsIncludingAlwaysVisible_supervisingProfile for HSUM

Modifies the test not to rely on the main user, since it may be
UserHandle.NULL on some builds.

Bug: 413580044
Test: atest
FrameworksMockingServicesTests: com.android.server.pm.UserManagerServiceMockedTest
Flag: android.multiuser.allow_supervising_profile
Change-Id: I95c24848bd0dbf1f6677f465728d55cc29cb0c8b