chore: Fix GDCH tests referencing obsolete GDCH audience methods #933

Job	Run time
filter	1m 9s
downstream-compatibility-spring-generator	11m 59s
downstream-compatibility (java-pubsublite)	3m 44s
downstream-compatibility (java-firestore)	5m 0s
downstream-compatibility (java-pubsub)	3m 41s
downstream-compatibility (java-bigtable)	4m 25s
	29m 58s

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