Fix CI to .NET 5

Author: anthony-c-martin

.github/workflows/main.yml

@@ -18,6 +18,8 @@ jobs:
 
       - name: Setup .NET Core
         uses: actions/[email protected]
+        with:
+          dotnet-version: '5.0.x'
 
       - name: Install NPM modules
         run: npm ci