[ML] Anomaly Detection Settings: Fix key attribute for filter list ta…

…ble (elastic#156392)

Fixes the React dev mode warning "Warning: Each child in a list should
have a unique "key" prop." by adding a key attribute to the
`DeleteFilterListModal` component.

x-pack/plugins/ml/public/application/settings/filter_lists/list/table.js

@@ -136,6 +136,7 @@ function renderToolsRight(
   return [
     <NewFilterButton key="new_filter_list" canCreateFilter={canCreateFilter} />,
     <DeleteFilterListModal
+      key="delete_filter_list"
       canDeleteFilter={canDeleteFilter}
       selectedFilterLists={selectedFilterLists}
       refreshFilterLists={refreshFilterLists}