Update phpstan/phpstan requirement from 1.10.67 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@1.10.67...1.12.6)

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

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

composer.json

@@ -54,7 +54,7 @@
         "php-stubs/wp-cli-stubs": "^2.8",
         "phpstan/extension-installer": "^1.3",
         "phpstan/phpdoc-parser": "^1.23.1",
-        "phpstan/phpstan": "1.10.67",
+        "phpstan/phpstan": "1.12.6",
         "phpunit/phpunit": "^9.3.3 || ^10.0.7 || ^11.0",
         "rector/rector": "^1.0",
         "squizlabs/php_codesniffer": "^3.7",