build(deps): upgrade grpc to 1.81.0 #18690

Job	Run time
package_name_check	59s
owlbot-yaml	1m 5s
gapic-bom	2m 40s
owlbot-py	1m 12s
group_id_check_for_maps_libraries	2m 52s
gitignore_correctness	59s
generate-readme	1m 5s
root-pom	1m 44s
	12m 36s

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