Coverage off in `test_zarr3.py`

[jakirkham]

It looks like test_zarr3.py is falling below coverage. Not sure what is expected to be covered or not here. So flagging it in an issue

https://app.codecov.io/gh/zarr-developers/numcodecs/blob/main/numcodecs%2Ftests%2Ftest_zarr3.py

[jakirkham]

Looks related to recent type hinting work in PR: #460

@dstansby do you know how we should handle this? Do we need to skip coverage on some lines or should they actually be covered somehow?

[dstansby]

These lines should be fixed by #633.