fix: disable certora for pull request runs as it will fail anyways

Author: sakulstra

.github/workflows/certora-stata.yml

@@ -13,7 +13,9 @@ on:
 jobs:
   verify:
     runs-on: ubuntu-latest
-
+    if:
+      github.event.pull_request.head.repo.full_name == github.repository || (github.event_name == 'push' &&
+      github.ref == format('refs/heads/{0}', github.event.repository.default_branch))
     steps:
       - uses: actions/checkout@v2
         with: