Adding getter/setter to clean the code

Author: leandrodamascena

aws_lambda_powertools/event_handler/openapi/params.py

@@ -632,8 +632,6 @@ def alias(self, value: Optional[str] = None):
             # This ensures that customers can access headers with any casing, as per the RFC guidelines.
             # Reference: https://www.rfc-editor.org/rfc/rfc7540#section-8.1.2
             self._alias = value.lower()
-        else:
-            self._alias = None
 
 
 class Body(FieldInfo):