Change the param type for UserHelper::hash_password() $algo to appease PHPStan.

PHPStan was complaining in 'plugins/auth_internal/init.php' due to UserHelper::hash_password() being passed a string, rather than a UserHelper::HASH_ALGO_* constant.  Just switching the param to string for now.

classes/userhelper.php

@@ -348,7 +348,7 @@ class UserHelper {
 	}
 
 	/**
-	 * @param UserHelper::HASH_ALGO_* $algo
+	 * @param string $algo should be one of UserHelper::HASH_ALGO_*
 	 *
 	 * @return false|string False if the password couldn't be hashed, otherwise the hash string.
 	 */