Update phpstan/phpstan requirement from 1.12.5 to 1.12.6

Updates the requirements on [phpstan/phpstan](https://github.com/phpstan/phpstan) to permit the latest version.
- [Release notes](https://github.com/phpstan/phpstan/releases)
- [Changelog](https://github.com/phpstan/phpstan/blob/2.0.x/CHANGELOG.md)
- [Commits](phpstan/phpstan@1.12.5...1.12.6)

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

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

composer.json

@@ -11,7 +11,7 @@
         "nethergamesmc/quiche": "dev-master"
     },
     "require-dev": {
-        "phpstan/phpstan": "1.12.5",
+        "phpstan/phpstan": "1.12.6",
         "nethergamesmc/pocketmine-mp": "dev-stable"
     },
     "repositories": [