Update phpstan/phpstan-phpunit requirement from ^1.3 to ^1.4

Updates the requirements on [phpstan/phpstan-phpunit](https://github.com/phpstan/phpstan-phpunit) to permit the latest version.
- [Release notes](https://github.com/phpstan/phpstan-phpunit/releases)
- [Commits](phpstan/phpstan-phpunit@1.3.0...1.4.0)

---
updated-dependencies:
- dependency-name: phpstan/phpstan-phpunit
  dependency-type: direct:development
...

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

composer.json

@@ -31,7 +31,7 @@
         "friendsofphp/php-cs-fixer": "^3.58",
         "phpstan/extension-installer": "^1.3",
         "phpstan/phpstan": "^1.11",
-        "phpstan/phpstan-phpunit": "^1.3",
+        "phpstan/phpstan-phpunit": "^1.4",
         "phpunit/phpunit": "^10.5",
         "spatie/ignition": "^1.14",
         "symfony/var-dumper": "^7.0",