SF: Fix unit tests for force_slower_follower_gpu_composition

Turning on force_slower_follower_gpu_composition breaks two tests, this
CL applies fixes by either turning the flag off so that we can change
the test when the flag is ready for cleanup or applies conditional
EXPECT_CALL.

Bug: 389982803
Flag: EXEMPT TEST_ONLY
Test: atest libcompositionengine_test with flag on
Change-Id: I96e516f188e97c935048fa52421d464191f584a2