Change xcode to c++20 #1450

Job	Run time
Set up and cache emscripten	9s
Copy the font files	4s
Build ubuntu-20.04-g++-10	3m 34s
Build ubuntu-20.04-g++-11	3m 38s
Build ubuntu-20.04-g++-12	22s
Build ubuntu-20.04-clang-10	3m 40s
Build ubuntu-20.04-clang-11	3m 35s
Build ubuntu-20.04-clang-12	3m 37s
Build macos-latest-xcode-13.1	3m 41s
Build macos-latest-xcode-14.2	3m 40s
Build macos-11-g++-12	3m 38s
Build JS toolkit (nohumdrum, Building toolkit without humdrum, -c -H -M, verovio-toolkit.js*)	3m 20s
Build JS toolkit (light, Building toolkit without humdrum as light version, -c -H -l -M, verovio-...	3m 22s
Build JS toolkit (wasm, Building toolkit without humdrum as wasm, -c -H -w -M, veroviowasm, true)	3m 23s
Build JS toolkit (default, Building default toolkit with humdrum, -c -M, -hum.js)	3m 22s
Build documentation	1s
Check settings for deployment	1s
Deploy documentation	1s
Deploy JS toolkit	1s
Skip deployment if set	1s
	43m 10s

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