Bump phpro/grumphp-shim from 2.14.0 to 2.15.0

Bumps [phpro/grumphp-shim](https://github.com/phpro/grumphp-shim) from 2.14.0 to 2.15.0.
- [Release notes](https://github.com/phpro/grumphp-shim/releases)
- [Commits](phpro/grumphp-shim@v2.14.0...v2.15.0)

---
updated-dependencies:
- dependency-name: phpro/grumphp-shim
  dependency-version: 2.15.0
  dependency-type: direct:development
  update-type: version-update:semver-minor
...

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

Author: dependabot[bot]