Handle missing record in after_delete_supplier_part (#12772) (#12777)

(cherry picked from commit 8c1c16e59a)

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

src/backend/InvenTree/company/models.py

@@ -1061,12 +1061,21 @@ def after_delete_supplier_part(sender, instance, **kwargs):
     Triggers a pricing update for the linked Part, so that removal of a
     supplier part is reflected in Part pricing and BOM cost rollups.
     """
+    from part.models import Part
+
     if (
-        InvenTree.ready.canAppAccessDatabase(allow_test=settings.TESTING_PRICING)
-        and not InvenTree.ready.isImportingData()
-        and instance.part
+        not InvenTree.ready.canAppAccessDatabase(allow_test=settings.TESTING_PRICING)
+        or InvenTree.ready.isImportingData()
+        or InvenTree.ready.isRunningMigrations()
     ):
-        instance.part.schedule_pricing_update(create=False)
+        return
+
+    try:
+        if part := instance.part:
+            part.schedule_pricing_update(create=False)
+    except (Part.DoesNotExist, SupplierPart.DoesNotExist):
+        # The underlying SupplierPart instance has been deleted
+        return
 
 
 @receiver(