github action do use dotnet sdk 6

Author: jakubmisek

.github/workflows/build-and-upload.yml

@@ -20,7 +20,8 @@ jobs:
     - name: Setup .NET Core
       uses: actions/setup-dotnet@v1
       with:
-        dotnet-version: 5.0.101
+        dotnet-version: '6.0.x'
+        include-prerelease: true
     - name: Build
       run: dotnet build -c ${{env.configuration}} -p:Version=${{env.version}}