Update PHPStan packages

| datasource | package                           | from    | to      |
| ---------- | --------------------------------- | ------- | ------- |
| packagist  | phpstan/extension-installer       | 1.2.0   | 1.4.3   |
| packagist  | phpstan/phpstan                   | 1.10.26 | 1.12.15 |
| packagist  | phpstan/phpstan-deprecation-rules | 1.1.3   | 1.2.1   |
| packagist  | phpstan/phpstan-phpunit           | 1.3.13  | 1.4.2   |
| packagist  | phpstan/phpstan-strict-rules      | 1.5.1   | 1.6.2   |

Author: renovate[bot]