chore: Fix GDCH tests referencing obsolete GDCH audience methods #19119

Job	Run time
gapic-libraries-bom	18m 23s
enforcer	18m 48s
lint	3m 6s
bulk-filter	1m 12s
changes	5s
windows	2m 35s
generation-config-check	1m 47s
split-units (sdk-platform-java, 8)	2m 54s
split-units (sdk-platform-java, 17)	6m 7s
split-units (sdk-platform-java, 21)	7m 3s
split-units (sdk-platform-java, 25)	6m 51s
split-units (sdk-platform-java, 11)	7m 39s
units (17)	32m 35s
units (11)	34m 39s
units (21)	32m 9s
units (25)	33m 59s
units (8)	34m 17s
	4h 4m 9s

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