fix: optimize fetching linked components for links

The link cannot have linked components, so avoid fetching it from the
database.

Fixes WEBLATE-27QC

weblate/trans/models/component.py

@@ -1996,6 +1996,8 @@ def get_repo_link_url(self):
     @cached_property
     def linked_childs(self) -> ComponentQuerySet:
         """Return list of components which links repository to us."""
+        if self.is_repo_link:
+            return self.component_set.none()
         children = self.component_set.prefetch()
         for child in children:
             child.linked_component = self