Missing-dependency error suggests `pip install pytorch_retinaface`, which is not a PyPI package

### Bug

`src/diffusers/utils/import_utils.py` tells users to install the optional RetinaFace dependency with:

> {0} requires the pytorch_retinaface library but it was not found in your environment. You can install it with pip: `pip install pytorch_retinaface`

`pip install pytorch_retinaface` cannot succeed: neither `pytorch_retinaface` nor its normalized form `pytorch-retinaface` exists on PyPI (both return HTTP 404 from `https://pypi.org/pypi//json`). The suggested command fails, and the name is currently unregistered on PyPI.

### Version

Present in v0.40.0 (`import_utils.py`, line 567).

### Reproduce

```
curl -s -o /dev/null -w '%{http_code}\n' https://pypi.org/pypi/pytorch_retinaface/json # 404
curl -s -o /dev/null -w '%{http_code}\n' https://pypi.org/pypi/pytorch-retinaface/json # 404
```

### Suggested fix

Point the message at the actual distribution of the `pytorch_retinaface` import (the intended project/source or the correct PyPI name), or drop the `pip install` hint if there is no canonical PyPI package.

Start in src/diffusers/utils/import_utils.py around line 567 and inspect the missing-dependency message for the pytorch_retinaface import. Verify the package name or source against the PyPI checks in the issue, then update the hint so it points to a valid installation path or omits the pip command; confirm the resulting error message with the relevant import-related tests.

Written by the indexing model from the issue text.