chore: fix verify_library_generation.yaml for forks #6443

Job	Run time
build(21) except self-service clients	11m 5s
build (11)	12m 18s
build (17)	12m 28s
build(8) except for gapic-generator-java	3m 56s
build(8) for gapic-generator-java	9m 10s
compatibility	1m 35s
gapic-generator-java-bom	1m 49s
lint	21s
showcase (11)	4m 12s
showcase-clirr	2m 58s
showcase (17)	3m 59s
showcase-native	8m 15s
dependency_analyzer_unit_test	13s
unmanaged_dependency_check	3m 55s
	1h 16m 14s

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