build(deps-dev): bump phpstan/phpstan from 0.12.48 to 0.12.50 (#50)

Bumps [phpstan/phpstan](https://github.com/phpstan/phpstan) from 0.12.48 to 0.12.50.
- [Release notes](https://github.com/phpstan/phpstan/releases)
- [Commits](phpstan/phpstan@0.12.48...0.12.50)

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

Author: dependabot[bot]