[skip ci] Restrict on-push freebsd build to main repo

The same applies to all other push jobs, it was just forgotten here.

Author: iluuu1994

.github/workflows/push.yml

@@ -171,6 +171,7 @@ jobs:
       - name: Test
         run: .github/scripts/windows/test.bat
   FREEBSD:
+    if: github.repository == 'php/php-src' || github.event_name == 'pull_request'
     name: FREEBSD
     runs-on: ubuntu-latest
     steps: