Move isAdminTestOnlyLocked inside synchronized block

Calling isAdminTestOnlyLocked outside the getLockObject
was causing error logs:
https://paste.googleplex.com/6318193934073856?raw

Bug: 167960209
Test: atest com.android.cts.devicepolicy.MixedDeviceOwnerTest#testSecondaryLockscreen
Change-Id: I2bbfd651f308859b3ff50d6dd63f5f19f5ce4558