Bump php-http/discovery from 1.14.2 to 1.15.3

Bumps [php-http/discovery](https://github.com/php-http/discovery) from 1.14.2 to 1.15.3.
- [Release notes](https://github.com/php-http/discovery/releases)
- [Changelog](https://github.com/php-http/discovery/blob/1.x/CHANGELOG.md)
- [Commits](php-http/discovery@1.14.2...1.15.3)

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

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