[Infra] Update shared-swift workflow to use macOS 15 for Xcode 16 #1450

Job	Run time
pod-lib-lint (ios, macos-14, Xcode_15.2)	6m 20s
pod-lib-lint (ios, macos-15, Xcode_16.1)	2m 2s
spm-package-resolved	1m 23s
pod-lib-lint (tvos, macos-14, Xcode_15.2)	1m 35s
pod-lib-lint (tvos, macos-15, Xcode_16.1)	1m 33s
pod-lib-lint (macos, macos-14, Xcode_15.2)	2m 17s
pod-lib-lint (macos, macos-15, Xcode_16.1)	1m 32s
pod-lib-lint (watchos, macos-14, Xcode_15.2)	1m 10s
pod-lib-lint (watchos, macos-15, Xcode_16.1)	1m 4s
spm (iOS, macos-14, Xcode_15.2)	7m 38s
spm (iOS, macos-15, Xcode_16.1)	2m 30s
spm (tvOS, macos-14, Xcode_15.2)	1m 54s
spm (tvOS, macos-15, Xcode_16.1)	1m 51s
spm (macOS, macos-14, Xcode_15.2)	2m 4s
spm (macOS, macos-15, Xcode_16.1)	2m 1s
spm (catalyst, macos-14, Xcode_15.2)	2m 9s
spm (catalyst, macos-15, Xcode_16.1)	2m 5s
spm (watchOS, macos-14, Xcode_15.2)	3m 42s
spm (watchOS, macos-15, Xcode_16.1)	2m 0s
	46m 50s

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