Update c-blosc to v1.26.1

[dstansby]

I'm not sure why, but in #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
• Tests pass locally
• [n/a] Docstrings and API docs for any new/modified user-facing classes and functions
• Changes documented in docs/release.rst
• [n/a] Docs build locally
• GitHub Actions CI passes
• Test coverage to 100% (Codecov passes)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.91%. Comparing base (dbc2975) to head (37d9786).
Report is 68 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #560   +/-   ##
=======================================
  Coverage   99.91%   99.91%           
=======================================
  Files          59       59           
  Lines        2334     2334           
=======================================
  Hits         2332     2332           
  Misses          2        2