append_asset - ensure to update existing rels appending second asset

E.g. in #5890 pset was shared by 2 elements and they it worked is
1) it appended first element and it's rel to pset
2) it appended second element and skipped updating it's rel as it was appended before. Now it's going to update it to ensure it encludes second element too.

I believe, issue occurred after 8c28f52 when we stopped duplicating inverses and started to reuse them.

src/ifcopenshell-python/ifcopenshell/api/project/append_asset.py

@@ -323,12 +323,16 @@ class Usecase:
 
         element_identity = element.wrapped_data.identity()
 
-        # check if inverse element were created before
-        if self.reuse_identities.get(element_identity) is not None:
-            return
-
-        new = self.file.create_entity(element.is_a())
-        self.reuse_identities[element_identity] = new
+        # Check if inverse element was created before.
+        # Still need to recreate it again - e.g. it could be some rel
+        # that now needs it's RelatingObjects to be extended by the current asset.
+        if (new := self.reuse_identities.get(element_identity)) is not None:
+            # Currently known cases requiring attributes reassignment are rels.
+            if not new.is_a("IfcRelationship"):
+                return
+        else:
+            new = self.file.create_entity(element.is_a())
+            self.reuse_identities[element_identity] = new
 
         for i, attribute in enumerate(element):
             new_attribute = None
@@ -346,11 +350,21 @@ class Usecase:
                 new[i] = new_attribute
 
     def is_another_asset(self, element: ifcopenshell.entity_instance) -> bool:
+        """Is IFC entity from inverse attribute is another asset to append that should be skipped."""
+
+        def by_guid(guid: str) -> Union[ifcopenshell.entity_instance, None]:
+            try:
+                return self.file.by_guid(guid)
+            except RuntimeError:
+                return None
+
         if element == self.settings["element"]:
             return False
         elif element.is_a("IfcFeatureElement"):
             # Feature elements match the target class but aren't considered "assets"
             return False
+        elif element.is_a("IfcRoot") and by_guid(element.GlobalId) is not None:
+            return False
         elif element.is_a(self.target_class):
             return True
         elif self.target_class == "IfcProduct" and element.is_a("IfcTypeProduct"):