Update phpstan/phpstan requirement from ^1.0 to ^1.8

Author: github-actions[bot]

composer.json

@@ -84,7 +84,7 @@
         "php-parallel-lint/php-parallel-lint": "^1.3",
         "phpbench/phpbench": "^1.2",
         "phpstan/extension-installer": "^1.1",
-        "phpstan/phpstan": "^1.0",
+        "phpstan/phpstan": "^1.8",
         "phpstan/phpstan-deprecation-rules": "^1.0",
         "phpstan/phpstan-phpunit": "^1.1",
         "phpstan/phpstan-strict-rules": "^1.0",