[DO NOT MERGE] Fix DozeScreenBrightnessTest.

This was broken by ag/15974634, but the presubmits did not catch that for some reason. That CL changed the brightness logic to be <= the dim value, so this failure (and fix) make sense.

Test: atest SystemUITests, since apparently treehugger won't do that and will +2 this anyway
Fixes: 202212576
Change-Id: Ibe18322fbe1e1fbae86c5274615ad0b6f727c8e2