Change AgentCard to use by_alias

Author: holtskinner

src/a2a/client/client.py

@@ -98,7 +98,9 @@ async def get_agent_card(
                 target_url,
                 agent_card_data,
             )
-            agent_card = AgentCard.model_validate(agent_card_data)
+            agent_card = AgentCard.model_validate(
+                agent_card_data, by_alias=True
+            )
         except httpx.HTTPStatusError as e:
             raise A2AClientHTTPError(
                 e.response.status_code,