Bump phpstan/phpstan-phpunit from 0.12.3 to 0.12.6

Bumps [phpstan/phpstan-phpunit](https://github.com/phpstan/phpstan-phpunit) from 0.12.3 to 0.12.6.
- [Release notes](https://github.com/phpstan/phpstan-phpunit/releases)
- [Commits](phpstan/phpstan-phpunit@0.12.3...0.12.6)

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

Author: dependabot-preview[bot]

composer.json

@@ -5,7 +5,7 @@
     "license": "MIT",
     "require": {
         "phpstan/phpstan": "0.12.9",
-        "phpstan/phpstan-phpunit": "0.12.3",
+        "phpstan/phpstan-phpunit": "0.12.6",
         "phpstan/phpstan-mockery": "^0.12.3",
         "phpstan/phpstan-webmozart-assert": "0.12.1",
         "phpstan/phpstan-php-parser": "^0.12.1"