GitHub: Add initial CI workflow #12

Job	Run time
formatting	37s
lib (Release, NWebDav.Server)	4m 9s
lib (Debug, Tmds.Fuse)	3m 31s
lib (Release, Tmds.Fuse)	3m 57s
lib (Release, NWebDav.Server.HttpListener)	5m 0s
lib (Debug, NWebDav.Server)	3m 20s
lib (Debug, NWebDav.Server.HttpListener)	3m 24s
	23m 58s

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