Update phpstan/phpstan requirement from ^1.11.5 to ^1.11.6 (MyIntervals#636)

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/1.11.x/CHANGELOG.md)
- [Commits](phpstan/phpstan@1.11.5...1.11.6)

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

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Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

composer.json

@@ -30,7 +30,7 @@
         "codacy/coverage": "^1.4.3",
         "php-parallel-lint/php-parallel-lint": "^1.4.0",
         "phpstan/extension-installer": "^1.4.1",
-        "phpstan/phpstan": "^1.11.5",
+        "phpstan/phpstan": "^1.11.6",
         "phpstan/phpstan-phpunit": "^1.4.0",
         "phpunit/phpunit": "^8.5.38",
         "rector/rector": "^1.1.1"