Update phpstan/phpstan requirement from ^1.11 to ^1.12

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/1.12.x/CHANGELOG.md)
- [Commits](phpstan/phpstan@1.11.0...1.12.0)

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

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

composer.json

@@ -42,7 +42,7 @@
     "php-http/psr7-integration-tests": "1.3.0",
     "phpspec/prophecy": "^1.19",
     "phpspec/prophecy-phpunit": "^2.2",
-    "phpstan/phpstan": "^1.11",
+    "phpstan/phpstan": "^1.12",
     "phpunit/phpunit": "^9.6",
     "squizlabs/php_codesniffer": "^3.10"
   },