Update phpstan/phpstan requirement from 1.12.0 to 1.12.3 (#268)

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@1.12.0...1.12.3)

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

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

composer.json

@@ -43,7 +43,7 @@
         "phpspec/prophecy": "dev-master as 1.19",
         "phpspec/prophecy-phpunit": "dev-master#0604e27 as 2.2.1",
         "phpstan/extension-installer": "^1.0",
-        "phpstan/phpstan": "1.12.0",
+        "phpstan/phpstan": "1.12.3",
         "phpstan/phpstan-phpunit": "^1.1",
         "phpunit/php-invoker": "^4.0||^5.0",
         "psalm/plugin-phpunit": "^0.19",