add support for .NET 8 #98

Job	Run time
build-micdemo-github-hosted (ubuntu-latest)	1m 2s
build-filedemo-github-hosted (ubuntu-latest)	56s
build-micdemo-github-hosted (windows-latest)	2m 2s
build-micdemo-self-hosted (rpi3-32)	2m 30s
build-filedemo-github-hosted (windows-latest)	1m 52s
build-micdemo-github-hosted (macos-latest)	1m 13s
build-micdemo-self-hosted (rpi3-64)	2m 59s
build-filedemo-github-hosted (macos-latest)	1m 8s
build-micdemo-self-hosted (rpi4-32)	1m 16s
build-micdemo-self-hosted (rpi4-64)	1m 31s
build-micdemo-self-hosted (rpi5-64)	36s
build-filedemo-self-hosted (rpi3-32)	1m 6s
build-filedemo-self-hosted (rpi3-64)	1m 19s
build-filedemo-self-hosted (rpi4-32)	33s
build-filedemo-self-hosted (rpi4-64)	36s
build-filedemo-self-hosted (rpi5-64)	1m 7s
	21m 46s

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