Update `macos-14` to `Xcode_16.0` as highest available #19

Job	Run time
build (ubuntu-22.04, g++-12, gcc-12, g++-12)	13m 41s
build (ubuntu-20.04, g++-9, gcc-9, g++-9)	14m 48s
build (ubuntu-22.04, clang-14, clang-14, clang++-14)	11m 3s
build (ubuntu-20.04, clang-9, clang-9, clang++-9, -fno-builtin)	9m 51s
build (macos-14, Xcode_16.0)	12m 32s
build (macos-13, Xcode_15.2)	18m 46s
build (macos-13, Xcode_14.3.1)	21m 18s
build (macos-12, Xcode_14.2)	14m 54s
	1h 56m 53s

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