Bump composer/composer from 2.1.6 to 2.1.9 in /tools/02_phpstan

Bumps [composer/composer](https://github.com/composer/composer) from 2.1.6 to 2.1.9.
- [Release notes](https://github.com/composer/composer/releases)
- [Changelog](https://github.com/composer/composer/blob/master/CHANGELOG.md)
- [Commits](composer/composer@2.1.6...2.1.9)

---
updated-dependencies:
- dependency-name: composer/composer
  dependency-type: indirect
...

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