BOM updates (#10611) (#10612)

* BOM updates

- Allow variants of substititute parts to be allocated
- Closes https://github.com/inventree/InvenTree/issues/10606

* Check self.allow_variants

* Add comment

(cherry picked from commit a7c4f2adba)

Co-authored-by: Oliver <oliver.henry.walters@gmail.com>

src/backend/InvenTree/part/models.py

@@ -4271,6 +4271,11 @@ class BomItem(InvenTree.models.MetadataMixin, InvenTree.models.InvenTreeModel):
             for sub in self.substitutes.all():
                 parts.add(sub.part)
 
+                # Account for variants of the substitute part (if allowed)
+                if allow_variants and self.allow_variants:
+                    for sub_variant in sub.part.get_descendants(include_self=False):
+                        parts.add(sub_variant)
+
         valid_parts = []
 
         for p in parts: