firebase-perf: fix API 34+ background-start heuristic in AppStartTrac… #6443

Job	Run time
Determine changed modules	1m 25s
Check all required Firestore tests results	2s
System Tests	0s
System Tests Against Nightly	0s
System Tests Against Emulator	-1s
System Tests With Enterprise DB	-1s
	1m 25s

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