fix(task_store): update task model dump mode to 'json' in API request… (kagent-dev#1031)

… (fixes tool call to github mcp server fails kagent-dev#976)

Signed-off-by: Peter Jausovec <peter.jausovec@solo.io>

Author: peterj

python/packages/kagent-core/src/kagent/core/a2a/_task_store.py

@@ -28,7 +28,7 @@ async def save(self, task: Task) -> None:
         Raises:
             httpx.HTTPStatusError: If the API request fails
         """
-        response = await self.client.post("/api/tasks", json=task.model_dump())
+        response = await self.client.post("/api/tasks", json=task.model_dump(mode="json"))
         response.raise_for_status()
 
     @override