ci: skip generate-tool-specs job on fork PRs

GitHub doesn't expose repo secrets to pull_request events from forks, so
${{ secrets.CREWAI_TOOL_SPECS_APP_ID }} resolves to an empty string and
tibdex/github-app-token@v2 errors with "Input required and not supplied:
app_id". The job also tries to push commits to the PR branch, which it
can't do on a fork regardless. Skip it for cross-repo PRs and keep it
for same-repo PRs and manual dispatch.

Co-authored-by: Greyson LaLonde <greyson.r.lalonde@gmail.com>

.github/workflows/generate-tool-specs.yml

@@ -14,6 +14,7 @@ permissions:
 
 jobs:
   generate-specs:
+    if: github.event_name == 'workflow_dispatch' || github.event.pull_request.head.repo.full_name == github.repository
     runs-on: ubuntu-latest
     env:
       PYTHONUNBUFFERED: 1