Reduce the color contrast requirements for the emphasized action button fill color.

This reduces the contrast requirement between the notification background and the button fill from 3:1 to 1.3:1

Fixes: 196393060
Test: manual testing using the go/notify2-apk and the CallStyle color customizer
Test: android.app.NotificationTest
Change-Id: I0fc3b7ae1ede7afd28974c59fa2a58d7fea2e9de