Fix the StockTilesRepository tests with different feature configs

We were filtering out the reduce brightness tile in the code, but the
corresponding tests were not updated. Therefore, we fix the tests with
testing different EvenDimmer feature flag status and configs.

Bug: 383266971
Test: atest StockTilesRepositoryTest
Flag: com.android.server.display.feature.flags.even_dimmer
Change-Id: Ia8531c8864649233487b5e98666324405a614307