Fix PowerIncidentTest

ag/9684175 changed mScreenBrightnessSettingMinimum,
mScreenBrightnessSettingMaximum and mScreenBrightnessSettingDefault
to float without changing proto dump and cts.

Bug: 149895022
Exempt-From-Owner-Approval: Minor change to fix CTS test
Test: atest CtsIncidentHostTestCases:com.android.server.cts.IncidentdTest#testIncidentReportDumpExplicit
Change-Id: Ief85ba8299626a3d92fb43db162a1b6864c8eae0