Revert fix to test unit tests

Author: holtskinner

src/a2a/client/client.py

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

src/a2a/server/apps/jsonrpc/jsonrpc_app.py

@@ -375,10 +375,7 @@ async def _handle_get_agent_card(self, request: Request) -> JSONResponse:
         # The public agent card is a direct serialization of the agent_card
         # provided at initialization.
         return JSONResponse(
-            self.agent_card.model_dump(
-                exclude_none=True,
-                by_alias=True,
-            )
+            self.agent_card.model_dump(mode='json', exclude_none=True)
         )
 
     async def _handle_get_authenticated_extended_agent_card(
@@ -395,8 +392,7 @@ async def _handle_get_authenticated_extended_agent_card(
         if self.extended_agent_card:
             return JSONResponse(
                 self.extended_agent_card.model_dump(
-                    exclude_none=True,
-                    by_alias=True,
+                    mode='json', exclude_none=True
                 )
             )
         # If supportsAuthenticatedExtendedCard is true, but no specific