Build(deps-dev): Bump phpstan/phpstan-phpunit from 0.12.5 to 0.12.6

Bumps [phpstan/phpstan-phpunit](https://github.com/phpstan/phpstan-phpunit) from 0.12.5 to 0.12.6.
- [Release notes](https://github.com/phpstan/phpstan-phpunit/releases)
- [Commits](phpstan/phpstan-phpunit@0.12.5...0.12.6)

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

Author: dependabot-preview[bot]

composer.json

@@ -26,7 +26,7 @@
     "phpstan/extension-installer": "^1.0.3",
     "phpstan/phpstan": "~0.12.5",
     "phpstan/phpstan-deprecation-rules": "~0.12.1",
-    "phpstan/phpstan-phpunit": "~0.12.5",
+    "phpstan/phpstan-phpunit": "~0.12.6",
     "phpstan/phpstan-strict-rules": "~0.12.1",
     "phpunit/phpunit": "^8.5.2",
     "psalm/plugin-phpunit": "~0.8.0",