Fix support for PDOExceptions (#1752)

When a PDOException is thrown (ex. Illuminate's QueryException) during the initialization of a Collector, the current code falls over because the code property on PDOExceptions are actually strings, and not ints. 

See [this comment from 15 years ago](https://www.php.net/manual/en/class.pdoexception.php#95812), php/php-src#9529, & php/php-src#12294

Author: LukeTowers

src/LaravelDebugbar.php

@@ -754,7 +754,7 @@ protected function addCollectorException(string $message, Exception $exception)
         $this->addThrowable(
             new Exception(
                 $message . ' on Laravel Debugbar: ' . $exception->getMessage(),
-                $exception->getCode(),
+                (int) $exception->getCode(),
                 $exception
             )
         );