Bump zizmor to 1.21.0

[martincostello]

Updated zizmor to 1.21.0.

[Copilot]

Pull request overview

This PR updates the zizmor linting tool from version 1.19.0 to 1.21.0 in the GitHub Actions workflow for linting.

Changes:

• Updated the ZIZMOR_VERSION environment variable from '1.19.0' to '1.21.0' in the lint workflow

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 96.15%. Comparing base (0ee3b96) to head (d91a63e).
⚠️ Report is 1 commits behind head on main.
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2905   +/-   ##
=======================================
  Coverage   96.15%   96.15%           
=======================================
  Files         309      309           
  Lines        7128     7128           
  Branches     1005     1005           
=======================================
  Hits         6854     6854           
  Misses        221      221           
  Partials       53       53           

Flag	Coverage Δ
linux	96.15% <ø> (ø)
macos	96.15% <ø> (ø)
windows	96.14% <ø> (ø)

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