workflows/teams: restrict to NixOS org

without the restriction the workflow would trigger on all forks,
but it is only relevant on NixOS/nixpkgs

.github/workflows/teams.yml

@@ -14,6 +14,7 @@ defaults:
 
 jobs:
   sync:
+    if: github.event_name != 'schedule' || github.repository_owner == 'NixOS'
     runs-on: ubuntu-24.04-arm
     steps:
       # Use a GitHub App to create the PR so that CI gets triggered and to