Bump phpstan/phpstan in the php-dev group across 1 directory

Bumps the php-dev group with 1 update in the / directory: [phpstan/phpstan](https://github.com/phpstan/phpstan).


Updates `phpstan/phpstan` from 1.12.19 to 1.12.20
- [Release notes](https://github.com/phpstan/phpstan/releases)
- [Changelog](https://github.com/phpstan/phpstan/blob/2.1.x/CHANGELOG.md)
- [Commits](phpstan/phpstan@1.12.19...1.12.20)

---
updated-dependencies:
- dependency-name: phpstan/phpstan
  dependency-type: direct:development
  update-type: version-update:semver-patch
  dependency-group: php-dev
...

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

Author: dependabot[bot]