Tighten EPSILON in BrightnessSynchronizer

This can be updated to smaller value, to make sure it's not equating 0-3% as the same value, since in that range the brightness value can get very small.

Bug: 408929889
Test: atest AutomaticBrightnessControllerTest
Flag: EXEMPT bug fix
Change-Id: I4bb9d4d5ae309f0e63d82b3daa7da5f516396156