chore(deps-dev): bump heroku/heroku-buildpack-php

Bumps [heroku/heroku-buildpack-php](https://github.com/heroku/heroku-buildpack-php) from 255 to 256.
- [Changelog](https://github.com/heroku/heroku-buildpack-php/blob/main/CHANGELOG.md)
- [Commits](heroku/heroku-buildpack-php@v255...v256)

---
updated-dependencies:
- dependency-name: heroku/heroku-buildpack-php
  dependency-type: direct:development
  update-type: version-update:semver-major
...

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