chore: bump webonyx/graphql-php from 15.13.0 to 15.18.0

Bumps [webonyx/graphql-php](https://github.com/webonyx/graphql-php) from 15.13.0 to 15.18.0.
- [Release notes](https://github.com/webonyx/graphql-php/releases)
- [Changelog](https://github.com/webonyx/graphql-php/blob/master/CHANGELOG.md)
- [Commits](webonyx/graphql-php@v15.13.0...v15.18.0)

---
updated-dependencies:
- dependency-name: webonyx/graphql-php
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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Author: dependabot[bot]