ci: Remove push-to-main triggers from CI workflows (#11406)
## Summary
- Removes `push: branches: [main]` triggers from `lint.yml`,
`test-js-packages.yml`, and `turborepo-test.yml`
- These workflows now only run on pull requests, avoiding redundant CI
runs after PRs are merged
- The `pr-clean-caches.yml` workflow retains its push trigger for cache
cleanup
