Test

Put `<janet.h>` include behind guard #1747

Job	Run time
Build and test on Windows (windows-latest)	45s
Build and test on POSIX systems (macos-13)	30s
Build and test on POSIX systems (macos-latest)	17s
Build on Windows with Mingw (CLANG64)	6h 0m 15s
Build and test with Mingw on Linux + Wine	3m 32s
Build and test on Windows Minimal build (windows-2022)	1m 7s
Build and test on POSIX systems (ubuntu-latest)	28s
Build on Windows with Mingw (UCRT64)	6h 0m 17s
Build and test on Windows (windows-2022)	48s
Build and test ARM32 cross compilation	2m 25s
Build and test s390x in qemu	3m 47s
	12h 14m 11s

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