refactor: Update .NET version in GitHub Actions workflow to 9.0.x

Author: foxminchan

.github/workflows/dotnetcore.yaml

@@ -11,12 +11,9 @@ jobs:
       - name: Setup .NET
         uses: actions/setup-dotnet@v4
         with:
-          dotnet-version: "8.0.x"
+          dotnet-version: "9.0.x"
           include-prerelease: true
 
-      - name: Install .NET Aspire workload
-        run: dotnet workload install aspire
-
       - name: Build & Restore
         run: dotnet build