fix(admin): fix FieldError on admin user change page

django/cantusdb_project/users/admin.py

@@ -11,7 +11,7 @@
 class SourceInline(admin.TabularInline):
     model = Source.current_editors.through
     raw_id_fields = ["source"]
-    ordering = ("holding_institution__siglum",)
+    ordering = ("source__holding_institution__siglum",)
     verbose_name_plural = "Sources assigned to User"