composer(deps-dev): update phpstan/phpstan requirement

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@0.12.80...0.12.81)

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

Author: dependabot[bot]

composer.json

@@ -21,7 +21,7 @@
     "mimmi20/coding-standard": "^2.0.1",
     "pepakriz/phpstan-exception-rules": "^0.11.6",
     "phpstan/extension-installer": "^1.1.0",
-    "phpstan/phpstan": "^0.12.80",
+    "phpstan/phpstan": "^0.12.81",
     "phpstan/phpstan-deprecation-rules": "^0.12.6"
   },
   "config": {