Failing to build a custom SM image based on sagemaker-distribution

### Category

Usability Issue

### 🐛 Describe the bug

Hi,
I'm trying to build a custom image based on the sagemaker-distribution on my Mac (silicon). I sarted with a simple Dockefile:
```Dockerfile
FROM public.ecr.aws/sagemaker/sagemaker-distribution:3.6-cpu

USER $MAMBA_USER
COPY --chown=$MAMBA_USER:$MAMBA_USER ./assets/conda-base-env.yml /tmp/environment.yml
RUN micromamba env update -n base -f /tmp/environment.yml && \
micromamba clean --all -f -y
```
My build fails with the following error:
```
RROR: failed to build: failed to solve: process "/usr/local/bin/_dockerfile_shell.sh micromamba env install -n base -f /tmp/environment.yml && micromamba clean --all -f -y" did not complete successfully: unable to find user sagemaker-user: no matching entries in passwd file
```

Any Ideas what could be the reason behind this error ?

### 🐛 Describe the expected behavior

_No response_

### Image Tags

3.6-cpu

Start by reproducing the Dockerfile build on a Mac with Apple silicon using the sagemaker-distribution:3.6-cpu image and assets/conda-base-env.yml. Check the USER and micromamba steps around the reported missing sagemaker-user entry. Done means the custom image builds successfully without the passwd-file error.

Written by the indexing model from the issue text.