Update dotnetdesktop.yml

Modifying to specify windows-2019 to see if this fixes my build issue first.

Author: wiredwiz

.github/workflows/dotnetdesktop.yml

@@ -4,7 +4,7 @@ on: [push]
 
 jobs:
   build:
-    runs-on: windows-latest
+    runs-on: windows-2019
 
     steps:
     - uses: actions/checkout@v1