Fix boundary condition for targetSDK gated changes

@EnabledAfter(targetSdk = FOO) means that apps targeting FOO should
still be able to override the change. Previously, the condition was
excluding FOO.

Bug: 156047625
Test: atest OverideValidatorImplTest
Change-Id: Ic0eecc83c9f96fb605b499579b9d58064dcaedd9