make perPage propTypes optional, because it's optional in interfaces

Author: adguernier

packages/ra-ui-materialui/src/list/InfiniteList.tsx

@@ -119,7 +119,7 @@ InfiniteList.propTypes = {
     ]),
     // @ts-ignore-line
     pagination: PropTypes.oneOfType([PropTypes.element, PropTypes.bool]),
-    perPage: PropTypes.number.isRequired,
+    perPage: PropTypes.number,
     //@ts-ignore-line
     sort: PropTypes.shape({
         field: PropTypes.string,