Bump symfony/phpunit-bridge from 5.3.4 to 5.3.7 in /vendor-bin/tools

Bumps [symfony/phpunit-bridge](https://github.com/symfony/phpunit-bridge) from 5.3.4 to 5.3.7.
- [Release notes](https://github.com/symfony/phpunit-bridge/releases)
- [Changelog](https://github.com/symfony/phpunit-bridge/blob/5.3/CHANGELOG.md)
- [Commits](symfony/phpunit-bridge@v5.3.4...v5.3.7)

---
updated-dependencies:
- dependency-name: symfony/phpunit-bridge
  dependency-type: direct:development
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <support@github.com>