Interrupt buffer in worker not working as expected when a custom stdout handler is set

## 🐛 Bug

When running python code using pyodide in a worker, with a custom stdout handler set, updating the interrupt buffer doesn't always stop execution immediately.

### To Reproduce

1. Have a pyodide worker with a sharedarraybuffer set as an interrupt buffer
2. Set a custom batch stdout function on the pyodide instance in the worker that posts a message on the worker
3. Run some python code that doesn't stop, such as:
```py
while 1:
print("Hello world")
```
4. Set the interruptBuffer[0] = 2
5. The worker continues to run for a while, continuing to send messages after you've set the interrupt buffer to keyboard interrupt

Repo with a minimal reproduction: https://github.com/alvesvaren/pyodide-worker-interrupt-issue

### Expected behavior

The execution stops immediately when I set the interrupt buffer to 2, and a KeyboardInterrupt error message is logged to the console.

### Environment

- Pyodide Version: 0.26.4
- Browser version: Firefox 133.0 (same issue in Chrome)
- Any other relevant information:

### Additional context

When running in chrome, it takes about the same amount of time for it to stop, but the "Cancelled worker"-message is sent when it's done printing messages up to that point, so I guess the messages might be queued or something.