switch to net6

Author: jogibear9988

.github/workflows/dotnet.yml

@@ -28,7 +28,7 @@ jobs:
     - name: Setup .NET
       uses: actions/setup-dotnet@v1
       with:
-        dotnet-version: 5.0.x
+        dotnet-version: 6.0.x
     - name: Setup NuGet.exe
       uses: nuget/setup-nuget@v1
     - run: nuget restore WpfDesign.sln