Fix errors detected by Ruff (#3918)

### What problem does this PR solve?

Fix errors detected by Ruff

### Type of change

- [x] Refactoring

api/db/services/api_service.py

@@ -64,7 +64,8 @@ class API4ConversationService(CommonService):
     @classmethod
     @DB.connection_context()
     def stats(cls, tenant_id, from_date, to_date, source=None):
-        if len(to_date) == 10: to_date += " 23:59:59"
+        if len(to_date) == 10:
+            to_date += " 23:59:59"
         return cls.model.select(
             cls.model.create_date.truncate("day").alias("dt"),
             peewee.fn.COUNT(