fix: don't touch caches if no-cache is given

[frostming]

Signed-off-by: Frost Ming me@frostming.com

Pull Request Checklist

• A news fragment is added in news/ describing what is new.
• Test cases added for changed code.

Describe what you have changed in this PR.

[codecov]

Codecov Report

Attention: Patch coverage is 75.75758% with 8 lines in your changes missing coverage. Please review.

Project coverage is 85.34%. Comparing base (28fd928) to head (5e4896f).
Report is 100 commits behind head on main.

Files	Patch %	Lines
src/pdm/models/caches.py	60.00%	4 Missing ⚠️
src/pdm/models/candidates.py	0.00%	2 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2913      +/-   ##
==========================================
- Coverage   85.36%   85.34%   -0.02%     
==========================================
  Files         106      106              
  Lines       10623    10629       +6     
  Branches     2313     2314       +1     
==========================================
+ Hits         9068     9071       +3     
- Misses       1089     1090       +1     
- Partials      466      468       +2     

Flag	Coverage Δ
unittests	85.12% <75.75%> (-0.02%)	⬇️

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