chore: refactor golden tests for autopopulation feature #5166

Job	Run time
build(8) except for gapic-generator-java	3m 29s
build(8) for gapic-generator-java	9m 48s
build (11)	12m 14s
build(21) except self-service clients	11m 5s
build (17)	11m 45s
compatibility	1m 35s
gapic-generator-java-bom	2m 8s
lint	26s
showcase (11)	4m 53s
showcase-clirr	3m 2s
showcase (17)	4m 48s
showcase-native	9m 40s
unmanaged_dependency_check	3m 26s
	1h 18m 19s

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