Removes .NET 5 from CI

Author: johnkors

.github/workflows/CI.yml

@@ -11,9 +11,7 @@ jobs:
       - name: Setup .NET
         uses: actions/setup-dotnet@v1
         with:
-          dotnet-version: |
-            5.0.x
-            6.0.x
+          dotnet-version: 6.0.x
       - name: Restore dependencies
         run: dotnet restore source
       - name: Build