Update secondary lockscreen tests.

Test: atest -c 'CtsDevicePolicyManagerTestCases:com.android.cts.devicepolicy.MixedDeviceOwnerTest#testSecondaryLockscreen'
Bug: 356895431
Bug: 361098832
Flag: android.app.admin.flags.secondary_lockscreen_api_enabled
Change-Id: Ie62d6b4b03b787884aa5a280094006750c6d8a73