Bump php-stubs/wordpress-stubs from 6.3.0 to 6.4.0

Bumps [php-stubs/wordpress-stubs](https://github.com/php-stubs/wordpress-stubs) from 6.3.0 to 6.4.0.
- [Release notes](https://github.com/php-stubs/wordpress-stubs/releases)
- [Commits](php-stubs/wordpress-stubs@v6.3.0...v6.4.0)

---
updated-dependencies:
- dependency-name: php-stubs/wordpress-stubs
  dependency-type: direct:development
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <[email protected]>