Passing configuration to `IPython.embed` and `IPython.embed_kernel`

Apologies if this is the wrong place to ask this, I tried on the gitter but it doesn't seem particularly active.

I'm trying to create an embedded ipython with a custom async loop runner. My naive attempt is something like:

```python
import IPython
from traitlets.config import Config
c = Config()
c.InteractiveShell.loop_runner = print # not a real runner, but enough to debug
IPython.embed(config=c)
```
but in the shell, `get_ipython().loop_runner` is still set to `IPython.core.async_helpers._pseudo_sync_runner`.

Am I setting the config wrongly, or is this config special and somehow harder to set?

Possibly a duplicate of https://github.com/ipython/ipython/issues/10724