ci: Use uv --frozen instead of --locked

[aborgna-q]

We'll try to use the current lock file, instead of failing if the uv.lock get's update (by e.g. a minor dependency bump)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 82.17%. Comparing base (ab4e006) to head (7b6be8d).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #677   +/-   ##
=======================================
  Coverage   82.17%   82.17%           
=======================================
  Files          50       50           
  Lines        6781     6781           
  Branches     6781     6781           
=======================================
  Hits         5572     5572           
  Misses        845      845           
  Partials      364      364           

Flag	Coverage Δ
rust	82.17% <ø> (ø)

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