Don't suppress pulsing notifications if we are already pulsing

When we receive a new alerting notification while we are already
pulsing, we make another request to DozeTriggers.requestPulse, which
rejects it, because we are already in a pulse state. This rejection
executes a callback, which removes our 2nd pulsing notification from the
alerting entries.

This CL allows calling DozeTriggers.requestPulse multiple times for new
notifications, without executing their suppression callback.

Fixes: 335560575
Test: atest DozeTriggersTest
Test: setup AOD, receive 2 pulsing notifications, check if the 2nd one
shows up
Flag: com.android.systemui.notification_pulsing_fix

Change-Id: I5e04e9d76ddf5df54ff05512b6645af29b9f238e