Update dotnet-desktop.yml

Upgrade framework version

Author: febinjoy

.github/workflows/dotnet-desktop.yml

@@ -71,7 +71,7 @@ jobs:
     - name: Install .NET Core
       uses: actions/setup-dotnet@v3
       with:
-        dotnet-version: 8.0.x
+        dotnet-version: 9.0.x
 
     # Add  MSBuild to the PATH: https://github.com/microsoft/setup-msbuild
     - name: Setup MSBuild.exe