fix(ReduceBrightColorsPreferenceController) Different feature configs

This change updates the tests for ReduceBrightColorsPreferenceController
to account for different combinations of feature flags and
configurations, specifically related to the "Even Dimmer" flag and the
availability of Reduce Bright Colors.

The updated tests ensure that the preference controller correctly
determines its availability based on these factors, improving test
coverage and reliability. This addresses inconsistencies between the
code and test cases, ensuring accurate behavior across various device
configurations.

Bug: 387071233
Test: atest ReduceBrightColorsPreferenceControllerTest
Flag: com.android.server.display.feature.flags.even_dimmer
Change-Id: Ie565ce996c7d4f49e194b119b32bf01a6508393e