Update CI to use the Xcode 16 release #434

Job	Run time
Library evolution	27s
Linux (debug)	47s
Examples (Debug, 15.4)	6m 9s
macOS (debug, 15.2)	57s
Linux (release)	48s
Examples (Debug, 16.0)	10m 16s
macOS (debug, 15.4)	57s
SwiftWasm (wasm-5.9.2-RELEASE)	4m 54s
Examples (Release, 15.4)	7m 11s
SwiftWasm (wasm-5.10.0-RELEASE)	48s
macOS (debug, 16.0)	1m 39s
Windows (windows-latest, debug)	1m 51s
Examples (Release, 16.0)	9m 38s
macOS (release, 15.2)	1m 4s
Windows (windows-latest, release)	2m 0s
macOS (release, 15.4)	40s
macOS (release, 16.0)	54s
	51m 0s

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