fix: Shared cache cannot support overlapping directory structures

[frostming]

Fixes #2105

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-commenter]

Codecov Report

Patch coverage: 100.00% and project coverage change: -0.01 ⚠️

Comparison is base (aaa6575) 84.50% compared to head (f8bfe6e) 84.50%.

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Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2106      +/-   ##
==========================================
- Coverage   84.50%   84.50%   -0.01%     
==========================================
  Files         100      100              
  Lines        9686     9685       -1     
  Branches     2128     2127       -1     
==========================================
- Hits         8185     8184       -1     
  Misses       1040     1040              
  Partials      461      461              

Flag	Coverage Δ
unittests	84.27% <100.00%> (-0.01%)	⬇️

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Impacted Files	Coverage Δ
src/pdm/installers/installers.py	80.13% <100.00%> (-0.14%)	⬇️

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