Add Xcode 15 CI for Storage #7876

Job	Run time
Check changed files	0s
binary_size_metrics (iOS)	7m 53s
pod-lib-lint-abtesting (iOS)	5m 58s
pod-lib-lint-auth (iOS)	8m 19s
pod-lib-lint-database (iOS)	10m 13s
pod-lib-lint-dynamiclinks (iOS)	9m 11s
pod-lib-lint-firestore (iOS)	24m 44s
pod-lib-lint-functions (iOS)	4m 50s
pod-lib-lint-inappmessaging (iOS)	9m 8s
pod-lib-lint-messaging (iOS)	12m 43s
pod-lib-lint-performance (iOS)	8m 13s
pod-lib-lint-remoteconfig (iOS)	13m 37s
pod-lib-lint-storage (iOS)	10m 56s
create_report	3m 35s
	2h 9m 20s

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