test: point to sdk-platform-java/.cloudbuild in generation IT #17772

Job	Run time
owlbot-yaml	1m 2s
gapic-bom	1m 57s
generate-readme	1m 12s
root-pom	1m 57s
package_name_check	1m 6s
group_id_check_for_maps_libraries	8m 29s
gitignore_correctness	1m 2s
owlbot-py	1m 17s
	18m 2s

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