fix: correctly mark a symlink as file to remove

[frostming]

Pull Request Check List

• 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.

Close #1580

[codecov-commenter]

Codecov Report

Base: 85.19% // Head: 85.20% // Increases project coverage by +0.00% 🎉

Coverage data is based on head (7c4d89d) compared to base (d8c4489).
Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1581   +/-   ##
=======================================
  Coverage   85.19%   85.20%           
=======================================
  Files          91       91           
  Lines        8100     8102    +2     
  Branches     1927     1928    +1     
=======================================
+ Hits         6901     6903    +2     
  Misses        807      807           
  Partials      392      392           

Flag	Coverage Δ
unittests	85.02% <100.00%> (+<0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
src/pdm/installers/uninstallers.py	80.82% <100.00%> (+0.20%)	⬆️

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