Fix store creation with latest zarr-python v3

[dstansby]

See failures at https://github.com/zarr-developers/numcodecs/pull/642.

[codecov[bot]]

Codecov Report

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

Project coverage is 99.81%. Comparing base (5b8c09c) to head (1cb02f7). Report is 1 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #644 +/- ## ========================================== + Coverage 90.08% 99.81% +9.73% ========================================== Files 62 62 Lines 2712 2712 ========================================== + Hits 2443 2707 +264 + Misses 269 5 -264 ``` | [Files with missing lines](https://app.codecov.io/gh/zarr-developers/numcodecs/pull/644?dropdown=coverage&src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=zarr-developers) | Coverage Δ | | |---|---|---| | [numcodecs/tests/test\_zarr3.py](https://app.codecov.io/gh/zarr-developers/numcodecs/pull/644?src=pr&el=tree&filepath=numcodecs%2Ftests%2Ftest_zarr3.py&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=zarr-developers#diff-bnVtY29kZWNzL3Rlc3RzL3Rlc3RfemFycjMucHk=) | `97.82% <100.00%> (+91.30%)` | :arrow_up: | ... and [1 file with indirect coverage changes](https://app.codecov.io/gh/zarr-developers/numcodecs/pull/644/indirect-changes?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=zarr-developers)

[jakirkham]

Thank you both! 🙏