`deprecated` creates bad docstring when passed a multiline message

### Report

Only the first line is indented, creating an invalid docstring: https://github.com/scverse/scanpy/pull/4109

```
docstring of […]filter_genes_dispersion:5: WARNING: Explicit markup ends without a blank line; unexpected unindent. [docutils] 
```

### Versions

```python
scverse-misc==0.0.5
```