do not use _bolder_ in admonitions

e.g. in 310_buffering.ipynb, admonitions are writte with double-asterix **:

```{admonition} **Example of Units**
:class: note, dropdown
- WGS 84 (EPSG Code:4326): **Degrees**.
- ETRS89 / UTM Zone 32N (EPSG Code:25832): **Meters**.
```

This leads to captions of admonitions being rendered as bolder