Bump bref/bref from 2.1.7 to 2.1.8 in /playground-runner (#649)

Bumps [bref/bref](https://github.com/brefphp/bref) from 2.1.7 to 2.1.8.
- [Release notes](https://github.com/brefphp/bref/releases)
- [Commits](brefphp/bref@2.1.7...2.1.8)

---
updated-dependencies:
- dependency-name: bref/bref
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]