ci - update actions to use node24

[commonism]

c.f. https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.86%. Comparing base (beeb15c) to head (26e3350).
⚠️ Report is 2 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #430   +/-   ##
=======================================
  Coverage   93.86%   93.86%           
=======================================
  Files         104      104           
  Lines        8397     8397           
=======================================
  Hits         7882     7882           
  Misses        515      515           

Flag	Coverage Δ
core	93.86% <ø> (ø)
extras	93.86% <ø> (ø)

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