Factor in overscroll in compose force QS expansion tests

We have a flag that prevents QS expansion on overscroll. We updated a
test class to consider overscroll when determining the expected
expansion value.

Flag: com.android.systemui.no_expansion_on_overscroll
Bug: 414346597
Test: atest QSFragmentComposeViewModelForceQSTest
Change-Id: I2fcfb14dd1a91da8871108a512e96cad86581c74