Test simplified entrypoint

The image currently uses a script which must be copied into the container: https://github.com/energy-quants/mambaforge/blob/09b1dbab3b446c69245cecd99fd217815af0cec8/build/images/docker-entrypoint.sh.

It may be sufficient to inline that into the `entrypoint` command?
```
buildah config --entrypoint '["/bin/bash", "-c", "$0 $@"]' "${container}"
```