composer(deps): Bump symfony/string from 6.3.8 to 6.4.0

Bumps [symfony/string](https://github.com/symfony/string) from 6.3.8 to 6.4.0.
- [Release notes](https://github.com/symfony/string/releases)
- [Changelog](https://github.com/symfony/string/blob/7.0/CHANGELOG.md)
- [Commits](symfony/string@v6.3.8...v6.4.0)

---
updated-dependencies:
- dependency-name: symfony/string
  dependency-type: indirect
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <support@github.com>