Update phpstan/phpstan-phpunit requirement from ^1.3.16 to ^1.4.0

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@1.3.16...1.4.0)

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

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

Author: dependabot[bot]

composer.json

@@ -30,7 +30,7 @@
         "codacy/coverage": "^1.4.3",
         "phpstan/extension-installer": "^1.3.1",
         "phpstan/phpstan": "^1.11.0",
-        "phpstan/phpstan-phpunit": "^1.3.16",
+        "phpstan/phpstan-phpunit": "^1.4.0",
         "phpunit/phpunit": "^8.5.38"
     },
     "suggest": {