[java-firestore] Flaky test ITShutdownTest#closeSuccess_withListenerRemove

[blakeli0]

ITShutdownTest#closeSuccess_withListenerRemove failed with the following errors in recent CIs

16:31:37:432 [ERROR] com.google.cloud.firestore.it.ITShutdownTest.closeSuccess_withListenerRemove -- Time elapsed: 5.044 s <<< ERROR!
org.junit.runners.model.TestTimedOutException: test timed out after 5 seconds
	at java.base@11.0.16/jdk.internal.misc.Unsafe.park(Native Method)

See error log for details.