build(deps): bump escapestudios/symfony2-coding-standard

Bumps [escapestudios/symfony2-coding-standard](https://github.com/djoos/Symfony-coding-standard) from 3.13.0 to 3.15.0.
- [Commits](djoos/Symfony-coding-standard@3.13.0...3.15.0)

---
updated-dependencies:
- dependency-name: escapestudios/symfony2-coding-standard
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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Author: dependabot[bot]