Update dotnetcore.yml to install .NET 9

Author: monoman

.github/workflows/dotnetcore.yml

@@ -10,10 +10,10 @@ jobs:
     steps:
     - uses: actions/checkout@v4
 
-    - name: Setup .NET 8.0
+    - name: Setup .NET 9.0
       uses: actions/setup-dotnet@v4
       with:
-        dotnet-version: 8.0.403    
+        dotnet-version: 9.0.201    
 
     - shell: bash
       run: dotnet build --configuration Release -v:m