Update get-a-github-vm.yaml

Author: nic-6443

.github/workflows/get-a-github-vm.yaml

@@ -10,7 +10,7 @@ on:
   workflow_dispatch:
 jobs:
   run:
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-20.04
     if: github.actor == github.event.repository.owner.login
     steps:
       - name: test