Drop support for Python 3.8

[afuetterer]

Feature request

This is not really a feature request nor a bug report. It is in between.

Python 3.8 reached EOL in October. I suggest dropping it.

Motivation

See #1942 and https://devguide.python.org/versions

Your contribution

Would you like me to submit a PR?

[afuetterer]

Also you will run into trouble, when dependencies only support 3.9+.

For example datamapplot is 3.9+ only.

[MaartenGr]

@afuetterer Thanks for sharing this! Fully agree, dropping support would be best as main dependencies are also dropping it (e.g., sentence-transformers). A PR would be appreciated!