[PHP]: Update phpstan/phpstan requirement from 1.12.7 to 1.12.8

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@1.12.7...1.12.8)

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

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

composer.json

@@ -32,7 +32,7 @@
     "require-dev": {
         "ext-ast": "*",
         "bamarni/composer-bin-plugin": "^1.4",
-        "phpstan/phpstan": "1.12.7",
+        "phpstan/phpstan": "1.12.8",
         "phpstan/phpstan-doctrine": "1.5.5",
         "phpstan/phpstan-phpunit": "1.4.0",
         "phpstan/phpstan-symfony": "1.4.12",