Fix nix workflow warning

[fspindle]

Magic Nix Cache is deprecated

Magic Nix Cache has been deprecated due to a change in the underlying GitHub APIs and will stop working on 1 February 2025. To continue caching Nix builds in GitHub Actions, use FlakeHub Cache instead.

Replace...
- uses: DeterminateSystems/magic-nix-cache-action@main

...with...
- uses: DeterminateSystems/flakehub-cache-action@main

For more details: https://dtr.mn/magic-nix-cache-eol

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 54.50%. Comparing base (0050c7e) to head (9fead73).
Report is 3 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1610      +/-   ##
==========================================
- Coverage   54.52%   54.50%   -0.02%     
==========================================
  Files         442      442              
  Lines       53480    53480              
==========================================
- Hits        29159    29150       -9     
- Misses      24321    24330       +9     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.