On Windows, use c++20 mode as correctly needed for designated initial… #4092

Job	Run time
KytheVerification	26s
KytheXrefs	0s
ClangTidy	1h 24m 46s
x86_64 test	10m 57s
MacOsBuild	50s
arm64 test	12m 27s
MacOsBuildDevTools	2m 11s
Generate Build matrix	6s
x86_64 test-nortti	13m 24s
PrepareVSPlugin	2m 7s
x86_64 test-c++20	15m 50s
VerifyFormatting	1m 32s
WindowsBuild	20m 12s
x86_64 test-c++23	15m 34s
x86_64 smoke-test	14m 10s
arm64 smoke-test	14m 31s
x86_64 smoke-test-analyzer	17m 32s
arm64 smoke-test-analyzer	17m 45s
x86_64 asan	21m 20s
x86_64 asan-clang	16m 51s
x86_64 compile	11m 34s
arm64 compile	7m 5s
x86_64 compile-clang	7m 9s
arm64 compile-clang	7m 27s
x86_64 compile-static	7m 1s
arm64 compile-static	6m 57s
x86_64 compile-static-clang	6m 54s
arm64 compile-static-clang	7m 19s
x86_64 coverage	17m 36s
x86_64 clean	6m 57s
arm64 clean	7m 14s
Build ·${{ matrix.arch }}:${{ matrix.os }}:${{ matrix.ver }}${{ (((matrix.link == 'static') && ':static') \|\| '') }}	0s
Build and deploy GitHub pages	0s
📦 Release	0s
	6h 15m 44s

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