chore: upgrade dotnet to 6 (#349)

Author: jonas-jonas

Dockerfile

@@ -89,7 +89,7 @@ RUN apt-get install -y --no-install-recommends \
 	zlib1g \
 	&& wget -O dotnet-install.sh https://dot.net/v1/dotnet-install.sh \
 	&& chmod +x dotnet-install.sh \
-	&& ./dotnet-install.sh --channel 5.0 \
+	&& ./dotnet-install.sh --channel 6.0 \
 	&& rm dotnet-install.sh
 
 # dart