Update c-blosc to v1.26.1

[dstansby]

I'm not sure why, but in https://github.com/zarr-developers/numcodecs/pull/501 c-blosc was updated to a commit that wasn't associated with a particular version. This PR updates c-blosc to v1.26.1, the latest release, which has updated versions of Zlib and Zstd.

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