Update phpstan/phpstan requirement from ^1.10.20 to ^1.10.21 (#867)

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](https://github.com/phpstan/phpstan/compare/1.10.20...1.10.21)

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

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

composer.json

@@ -41,7 +41,7 @@
 		"helmich/typo3-typoscript-lint": "^3.1.0",
 		"php-coveralls/php-coveralls": "^2.5.3",
 		"phpstan/extension-installer": "^1.3.1",
-		"phpstan/phpstan": "^1.10.20",
+		"phpstan/phpstan": "^1.10.21",
 		"phpstan/phpstan-phpunit": "^1.3.13",
 		"phpstan/phpstan-strict-rules": "^1.5.1",
 		"phpunit/phpunit": "^9.6.9",