ci: correct working-directory in sdk-platform-java-verify_library_generation.yaml #17137

Job	Run time
package_name_check	1m 1s
gitignore_correctness	1m 2s
root-pom	1m 34s
group_id_check_for_maps_libraries	7m 10s
owlbot-py	1m 8s
gapic-bom	1m 33s
generate-readme	1m 4s
owlbot-yaml	59s
	15m 31s

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