[App Check] Fix warning due to NSUInteger length on watchOS #7794

Job	Run time
Check changed files	0s
pod-lib-lint-auth (iOS)	8m 53s
binary_size_metrics (iOS)	8m 11s
pod-lib-lint-abtesting (iOS)	7m 6s
pod-lib-lint-dynamiclinks (iOS)	5m 34s
pod-lib-lint-database (iOS)	14m 18s
pod-lib-lint-functions (iOS)	3m 0s
pod-lib-lint-inappmessaging (iOS)	8m 36s
pod-lib-lint-firestore (iOS)	42m 53s
pod-lib-lint-messaging (iOS)	7m 48s
pod-lib-lint-performance (iOS)	9m 59s
pod-lib-lint-remoteconfig (iOS)	8m 55s
pod-lib-lint-storage (iOS)	8m 28s
create_report	4m 28s
	2h 18m 9s

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