ci: configure the protected branch #14439

Job	Run time
gapic-bom	1m 18s
root-pom	1m 16s
owlbot-yaml	35s
owlbot-py	43s
generate-readme	41s
package_name_check	35s
gitignore_correctness	34s
group_id_check_for_maps_libraries	5m 56s
	11m 38s

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