Update YAML to install .NET6

.github/workflows/ci.yml

@@ -30,7 +30,7 @@ jobs:
     - name: Setup .NET
       uses: actions/setup-dotnet@v1
       with:
-        dotnet-version: 5.0.x
+        dotnet-version: 6.0.x
 
     - name: Restore dependencies
       run: dotnet restore $env:Solution_Name