Update dotnet-desktop.yml for .net 8

Author: LeftofZen

.github/workflows/dotnet-desktop.yml

@@ -73,7 +73,7 @@ jobs:
     - name: Install .NET
       uses: actions/setup-dotnet@v3
       with:
-        dotnet-version: 7.0.x
+        dotnet-version: 8.0.x
 
     # Execute all unit tests in the solution
     #- name: Execute unit tests