Fix Black formatting in entities.py

Remove trailing space to pass lint check.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: vahid-ahmadi

policyengine_uk/entities.py

@@ -3,7 +3,7 @@
 # This file defines the entities needed by our legislation.
 from policyengine_core.entities import build_entity
 
-Household = build_entity( 
+Household = build_entity(
     key="household",
     plural="households",
     label="Household",