Bump composer/composer in /tests/Composer/__fixtures__

Bumps [composer/composer](https://github.com/composer/composer) from 2.9.5 to 2.9.6.
- [Release notes](https://github.com/composer/composer/releases)
- [Changelog](https://github.com/composer/composer/blob/main/CHANGELOG.md)
- [Commits](composer/composer@2.9.5...2.9.6)

---
updated-dependencies:
- dependency-name: composer/composer
  dependency-version: 2.9.6
  dependency-type: direct:production
...

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Author: dependabot[bot]