Drop support for Python 3.8

[dstansby]

As per SPEC 0, don't need to support Python 3.8 or 3.9 any more. As per a comment below, I've only dropped support for 3.8 here.

[codecov[bot]]

Codecov Report

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

Project coverage is 85.70%. Comparing base (b5f8506) to head (2e44a8e). Report is 21 commits behind head on master.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #381 +/- ## ========================================== - Coverage 85.82% 85.70% -0.13% ========================================== Files 13 13 Lines 1538 1539 +1 ========================================== - Hits 1320 1319 -1 - Misses 218 220 +2 ```

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[joshmoore]

Thanks, @dstansby. I've recently heard of folks having issues on various platforms so let's see if any of that surfaces here. If not, I can definitely see getting this into the next largish bump.

[will-moore]

I was having issues getting Ice bindings installed on python 3.10 (our docs state that only python 3.9 was supported). In the end we found a work-around but for users who have working python 3.9 environments it could cause inconvenience to drop python 3.9 support here before we need to. Happy to drop 3.8 support, but dropping 3.9 support feels a little early (unless supporting it is a burden to us that we are keen to drop?)

[dstansby]

The motivation here was zarr follows SPEC 0, so won't (in theory) be supporting Python 3.8/3.9 now anyway, so it makes sense to mirror that here? Happy to change this to just drop 3.8 though.

[dstansby]

👍 updated to just drop support for 3.8

[joshmoore]

Thanks again, @dstansby. Let's get this in and then we can always iterate from there.