Promote TaplTestsQuickstep.testBackground to presubmit

- http://android-build/test_hub/search/?filter=&invfilter=unhealthyInvocations&invfilter=staleInvocations&query=test%3Acom.android.quickstep.TaplTestsQuickstep%23testBackground
- Latest result is <0.5% flaky

Bug: 364036214
Test: presubmit
Flag: EXEMPT TEST_ONLY
Change-Id: I97315a23e09c75a5f72cd3f6c959607598d9222d