Switch to python 3.9 in dev-deps CI matrix run since dev deps are now beginning to drop Python 3.8 which is EOL soon

[asmacdo]

Fixes https://github.com/dandi/dandi-cli/issues/1503

[codecov[bot]]

Codecov Report

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

Project coverage is 88.63%. Comparing base (d5c4a3f) to head (faff2f6). Report is 46 commits behind head on master.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #1506 +/- ## ========================================== + Coverage 88.56% 88.63% +0.07% ========================================== Files 77 77 Lines 10572 10572 ========================================== + Hits 9363 9371 +8 + Misses 1209 1201 -8 ``` | [Flag](https://app.codecov.io/gh/dandi/dandi-cli/pull/1506/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=dandi) | Coverage Δ | | |---|---|---| | [unittests](https://app.codecov.io/gh/dandi/dandi-cli/pull/1506/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=dandi) | `88.63% <ø> (+0.07%)` | :arrow_up: | 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=dandi#carryforward-flags-in-the-pull-request-comment) to find out more.

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[yarikoptic]

added a label for auto , and adjusted PR title so it is descriptive of the change whenever it gets into CHANGELOG. dev-deps is green, let's proceed

[github-actions[bot]]

:rocket: PR was released in 0.64.0 :rocket: