Update dotnet-desktop.yml

ok i will not directly push to master ever again

Author: AsertCreator

.github/workflows/dotnet-desktop.yml

@@ -2,6 +2,8 @@ on:
   push:
     branches:
       - master
+  pull_request:
+    types: [opened, synchronize, reopened]
 jobs:
   test-build:
     name: BUILD