Update phpstan/phpstan requirement from 0.12.85 to 0.12.88

Updates the requirements on [phpstan/phpstan](https://github.com/phpstan/phpstan) to permit the latest version.
- [Release notes](https://github.com/phpstan/phpstan/releases)
- [Commits](phpstan/phpstan@0.12.85...0.12.88)

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

composer.json

@@ -23,7 +23,7 @@
     "require-dev": {
         "nette/tester": "2.4.0",
         "mockery/mockery": "1.4.3",
-        "phpstan/phpstan": "0.12.85",
+        "phpstan/phpstan": "0.12.88",
         "phpstan/phpstan-strict-rules": "0.12.9",
         "pepakriz/phpstan-exception-rules": "0.11.6",
         "phpstan/phpstan-nette": "0.12.16",