Allow any value to be passed to Assertion::isCountable() (#303)

* Allow any value to be passed to Assertion::isCountable()

Static analysis tools complain about type of `$value` argument but in fact it could be of any type since it will be checked later (that's the purpose of the method).

* Revert unwanted changes

Github's web IDE did something weird I think, I did not change those line on purpose (obviously).

lib/Assert/Assertion.php

@@ -1233,7 +1233,7 @@ public static function isArrayAccessible($value, $message = null, string $proper
     /**
      * Assert that value is countable.
      *
-     * @param array|Countable|ResourceBundle|SimpleXMLElement $value
+     * @param mixed $value
      * @param string|callable|null $message
      * @param string|null $propertyPath
      *