Update dotnet-core.yml

.github/workflows/dotnet-core.yml

@@ -16,7 +16,7 @@ jobs:
     - name: Setup .NET Core
       uses: actions/setup-dotnet@v1
       with:
-        dotnet-version: 3.1.200
+        dotnet-version: 5.0.400
     - name: Install dependencies
       run: |
            cd "C:\Program Files (x86)\Microsoft Visual Studio\2019\Enterprise\MSBuild\Current\Bin\"