GithubCI: switch to MacOS 13 #4148

Job	Run time
macOS--dotnet6-only	4m 51s
macOS--dotnet6-and-mono	8m 25s
linux22-github--dotnet-and-mono	3m 59s
macOS--mono-only	16m 2s
linux22-github--dotnet-and-newmono	3m 59s
linux22-vanilla--stockmono-only	5m 49s
windows--dotnet6-and-legacyFramework	5m 4s
windows--dotnet6-only	6m 30s
windows--legacyFramework-only	8m 49s
linux20-github--dotnet-and-mono	4m 0s
linux20-vanilla--newmono-only	6m 18s
linux20-github--dotnet-and-newmono	4m 8s
linux20-vanilla--stockmono-only	5m 43s
linux22-vanilla--newmono-only	6m 23s
linux22-vanilla--stockdotnet6-and-newmono	6m 12s
linux22-vanilla--stockdotnet6-and-stockmono	5m 20s
linux22-vanilla--stockdotnet6-only	5m 12s
conventions	1m 26s
snap_pkg	4m 14s
	1h 52m 24s

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