deps: update googleapis/java-cloud-bom digest to ac9893c #5275

Job	Run time
build(8) except for gapic-generator-java	3m 28s
build (11)	11m 46s
build (17)	11m 41s
build(21) except self-service clients	10m 45s
build(8) for gapic-generator-java	9m 53s
compatibility	1m 47s
gapic-generator-java-bom	1m 42s
lint	23s
showcase (11)	4m 56s
showcase-clirr	3m 14s
showcase (17)	4m 39s
showcase-native	9m 36s
unmanaged_dependency_check	4m 17s
	1h 18m 7s

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