[Autofill CTS] Mark critical tests in OptionalSaveActivityTest for internal tracking purpose

OptionalSaveActivityTest is mainly testing required_id and optional_id is working as expected 

Test: atest CtsAutoFillServiceTestCase
Bug: b/424612157
Flag: EXEMPT TEST_ONLY
Change-Id: Idfa89a52d5ff2577cd3e3a2c8f112a495da513cb
1 file changed