add some PHPStan-specific callable prototypes

src/pocketmine/utils/Internet.php

@@ -183,6 +183,7 @@ class Internet{
 	 * @param string[]      $extraHeaders extra headers to send as a plain string array
 	 * @param array         $extraOpts    extra CURLOPT_* to set as an [opt => value] map
 	 * @param callable|null $onSuccess    function to be called if there is no error. Accepts a resource argument as the cURL handle.
+	 * @phpstan-param (callable(resource) : void)|null $onSuccess
 	 *
 	 * @return array a plain array of three [result body : string, headers : array[], HTTP response code : int]. Headers are grouped by requests with strtolower(header name) as keys and header value as values
 	 *