Fix flakiness of TextToSpeechTest

... 2nd attempt.
Previously, the test was failing because player "idle" state is
not always received.
We expect "started" state to be always received with successfull
TTS invocation.

Test: atest TextToSpeech
Bug: 306200508
Bug: 307751040
Change-Id: I73142790fc75829d79ea8c37c6aefd5372e25d2a
1 file changed