Run lock issues/PRs only on getsentry (#1966)

Author: aminvakil

.github/workflows/lock.yml

@@ -5,6 +5,7 @@ on:
   workflow_dispatch:
 jobs:
   lock:
+    if: github.repository_owner == 'getsentry'
     runs-on: ubuntu-latest
     steps:
       - uses: getsentry/forked-action-lock-threads@master