api!(deltachat-jsonrpc): use kind as a tag for all union types

deltachat-rpc-client/tests/test_webxdc.py

@@ -13,7 +13,7 @@ async def test_webxdc(acfactory) -> None:
 
     while True:
         event = await bob.wait_for_event()
-        if event.type == EventType.INCOMING_MSG:
+        if event.kind == EventType.INCOMING_MSG:
             bob_chat_alice = bob.get_chat_by_id(event.chat_id)
             message = bob.get_message_by_id(event.msg_id)
             break