ci: configure the protected branch #14542

Job	Run time
gapic-bom	1m 10s
root-pom	1m 9s
owlbot-yaml	33s
owlbot-py	43s
generate-readme	41s
gitignore_correctness	34s
group_id_check_for_maps_libraries	6m 6s
package_name_check	34s
	11m 30s

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