typing fix

Author: holtskinner

src/a2a/server/request_handlers/grpc_handler.py

@@ -289,7 +289,7 @@ async def GetAgentCard(
 
     async def abort_context(
         self, error: ServerError, context: grpc.ServicerContext
-    ):
+    ) -> None:
         match error.error:
             case types.JSONParseError():
                 await context.abort(