Fix error in CI jobs

[DimitriPapadopoulos]

Fixes this error:

▼ Run conda activate env
  conda activate env
  flake8
  shell: /usr/bin/bash -l {0}
  env:
    INPUT_RUN_POST: true
    CONDA_PKGS_DIR: /home/runner/conda_pkgs_dir
./numcodecs/version.py:5:5: F[4](https://github.com/zarr-developers/numcodecs/actions/runs/6349262059/job/17247197031?pr=467#step:9:4)01 'typing.Tuple' imported but unused
Error: Process completed with exit code 1.

Pinning setuptools-scm to a newer version might also fix this issue at some point (pypa/setuptools-scm#482 (comment)), but in any case having linters skip generated files beyond our control is good practice.

TODO:

• Unit tests and/or doctests in docstrings
• Tests pass locally
• Docstrings and API docs for any new/modified user-facing classes and functions
• Changes documented in docs/release.rst
• Docs build locally
• GitHub Actions CI passes
• Test coverage to 100% (Codecov passes)

[joshmoore]

Struggling with the OSX builds which are unrelated, so merging proactively.