chore: Fix GDCH tests referencing obsolete GDCH audience methods #927

Job	Run time
filter	1m 0s
downstream-compatibility-spring-generator	12m 3s
downstream-compatibility (java-firestore)	5m 11s
downstream-compatibility (java-pubsublite)	4m 19s
downstream-compatibility (java-pubsub)	4m 42s
downstream-compatibility (java-bigtable)	4m 33s
	31m 48s

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