Update overflow dot color when app icon flag is on

Previously we weren't applying colors at all to any icons, including the
overflow dot (which should still be updated).

Bug: 335211019
Test: manually check that the dot color is correct
Flag: ACONFIG android.app.notifications_use_app_icon DEVELOPMENT
Change-Id: I2fb29d4734c7eab7026fbc68001a710b9a5a0827