remove ineffective cache mount lines

[EmilyRagan]

What changed

Removed Docker cache mounts for uv

Why it changed

They were being overridden by UV_CACHE_DIR already, cache mounts were misleading

Testing strategy

openc3.sh build

Review notes

n/a

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 79.40%. Comparing base (64205c4) to head (bdab26b).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3840      +/-   ##
==========================================
+ Coverage   79.38%   79.40%   +0.01%     
==========================================
  Files         897      897              
  Lines       67605    67614       +9     
  Branches     2658     2610      -48     
==========================================
+ Hits        53666    53686      +20     
+ Misses      13266    13259       -7     
+ Partials      673      669       -4     

Flag	Coverage Δ
frontend	66.54% <ø> (+0.02%)	⬆️
python	79.41% <ø> (-0.01%)	⬇️
ruby-api	82.22% <ø> (+0.24%)	⬆️
ruby-backend	84.75% <ø> (ø)

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[sonarqubecloud]

Quality Gate failed

Failed conditions
Vulnerabilities with severity Major found (required < Minor)
Code smells with severity Major found (required < Major)

See analysis details on SonarQube Cloud