Update seaborn theme names for Matplotlib >= 3.6.0

Matplotlib renamed the seaborn styles from e.g. seaborn-colorblind to seaborn-v0_8-colorblind.

Fixes #874 (closed).

See:

• https://matplotlib.org/stable/api/prev_api_changes/api_changes_3.6.0.html#seaborn-styles-renamed
• https://matplotlib.org/stable/api/prev_api_changes/api_changes_3.8.0.html#removal-of-deprecated-apis