Bump gecko-packages/gecko-php-unit from 3.0 to 3.1

Bumps [gecko-packages/gecko-php-unit](https://github.com/GeckoPackages/GeckoPHPUnit) from 3.0 to 3.1.
- [Release notes](https://github.com/GeckoPackages/GeckoPHPUnit/releases)
- [Changelog](https://github.com/GeckoPackages/GeckoPHPUnit/blob/3.0/CHANGELOG.md)
- [Commits](GeckoPackages/GeckoPHPUnit@v3.0...v3.1)

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

Author: dependabot-support