Updated the workflow to be compatible with .NET 5

Author: NinjaCheetah

.github/workflows/dotnet-core.yml

@@ -16,7 +16,7 @@ jobs:
     - name: Setup .NET Core
       uses: actions/setup-dotnet@v1
       with:
-        dotnet-version: 3.1.101
+        dotnet-version: 5.0.100
     - name: Install dependencies
       run: dotnet restore
     - name: Build