refactor: streamline code formatting in API and tests

- Consolidated function call formatting in `admin_reassign_duty` for improved readability.
- Enhanced test cases by standardizing header formatting in API requests, ensuring consistency across tests.
- Improved overall code clarity and maintainability by adhering to established coding style guidelines.

duty_teller/api/app.py

@@ -374,9 +374,7 @@ def admin_reassign_duty(
             status_code=400,
             detail=t(lang, "admin.user_not_found"),
         )
-    updated = update_duty_user(
-        session, duty_id, body.user_id, commit=True
-    )
+    updated = update_duty_user(session, duty_id, body.user_id, commit=True)
     if updated is None:
         raise HTTPException(
             status_code=404,