Add Xcode 15 CI for Storage #5981

Job	Run time
changes	3s
spm-binary-cron	0s
check	3m 52s
cmake (macos-12)	26m 31s
sanitizers (macos-12, asan)	31m 50s
cmake (ubuntu-latest)	20m 36s
sanitizers (macos-12, tsan)	24m 41s
xcodebuild (iOS)	27m 29s
cmake-prod-db (macos-12, (default))	26m 44s
xcodebuild (tvOS)	40m 10s
cmake-prod-db (macos-12, test-db)	29m 37s
xcodebuild (macOS)	29m 47s
pod-lib-lint (FirebaseFirestoreInternal.podspec)	25m 47s
pod-lib-lint-cron	0s
pod-lib-lint (FirebaseFirestore.podspec)	25m 9s
spm-binary	5m 14s
pod-lib-lint (FirebaseFirestoreSwift.podspec)	20m 53s
spm-source	20m 16s
Check all required Firestore tests results	1s
	5h 58m 40s

Provide feedback