Update dotnet version and apply clean fix

Author: Matthiee

.github/workflows/dotnet-core.yml

@@ -16,7 +16,9 @@ jobs:
     - name: Setup .NET Core
       uses: actions/setup-dotnet@v1
       with:
-        dotnet-version: 3.1.301
+        dotnet-version: 5.0.101
+    - name: Clean
+      run: dotnet clean -c Release
     - name: Install dependencies
       run: dotnet restore
     - name: Build