Bump phpbench/phpbench from 1.2.7 to 1.2.8 in /tools (#441)

Bumps [phpbench/phpbench](https://github.com/phpbench/phpbench) from 1.2.7 to 1.2.8.
- [Release notes](https://github.com/phpbench/phpbench/releases)
- [Changelog](https://github.com/phpbench/phpbench/blob/master/CHANGELOG.md)
- [Commits](phpbench/phpbench@1.2.7...1.2.8)

---
updated-dependencies:
- dependency-name: phpbench/phpbench
  dependency-type: direct:development
  update-type: version-update:semver-patch
...

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

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