build(deps): upgrade grpc to 1.81.0 #1912

Job	Run time
filter	1m 6s
downstream-compatibility (spring-cloud-gcp)	11m 53s
downstream-compatibility (java-bigtable)	8m 58s
downstream-compatibility (java-firestore)	4m 41s
downstream-compatibility (java-pubsub)	4m 13s
downstream-compatibility (java-pubsublite)	3m 58s
conditional-required-check	4s
	34m 53s

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