drop py37 py38 and update dependencies

[mathause]

• [ ] Closes #xxx
• [ ] Tests added
• [ ] Passes isort . && black . && flake8
• [ ] Fully documented, including CHANGELOG.md

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (a28596f) 94.80% compared to head (d1f2bad) 94.75%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #88 +/- ## ========================================== - Coverage 94.80% 94.75% -0.06% ========================================== Files 7 7 Lines 385 381 -4 ========================================== - Hits 365 361 -4 Misses 20 20 ``` | [Flag](https://app.codecov.io/gh/mathause/mplotutils/pull/88/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Mathias+Hauser) | Coverage Δ | | |---|---|---| | [min-all-deps](https://app.codecov.io/gh/mathause/mplotutils/pull/88/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Mathias+Hauser) | `94.75% <100.00%> (-0.05%)` | :arrow_down: | | [unittests](https://app.codecov.io/gh/mathause/mplotutils/pull/88/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Mathias+Hauser) | `94.75% <100.00%> (-0.06%)` | :arrow_down: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Mathias+Hauser#carryforward-flags-in-the-pull-request-comment) to find out more.

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