Bump symfony/http-client from 6.4.14 to 6.4.15 in /webapp

Bumps [symfony/http-client](https://github.com/symfony/http-client) from 6.4.14 to 6.4.15.
- [Release notes](https://github.com/symfony/http-client/releases)
- [Changelog](https://github.com/symfony/http-client/blob/7.1/CHANGELOG.md)
- [Commits](symfony/http-client@v6.4.14...v6.4.15)

---
updated-dependencies:
- dependency-name: symfony/http-client
  dependency-type: direct:production
...

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Author: dependabot[bot]