Speed up tests mocking PermissionControllerApplication

Mocking static methods of final classes is significantly faster than
static method of non-final classes. For PermissionControllerApplication
it does not matter, hence mark it as final.

Bug: 155019930
Test: atest RuntimePermissionsUpgradeControllerTest
Change-Id: If8099dc276695f77bb47e84dc2a14e53dd1fd97d
Merged-In: If8099dc276695f77bb47e84dc2a14e53dd1fd97d