fix(dotnet): use 5.0 channel

Author: aeneasr

Dockerfile

@@ -84,7 +84,7 @@ 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 Current \
+	&& ./dotnet-install.sh --channel 5.0 \
 	&& rm dotnet-install.sh
 
 # dart