fix: correct the comparison of candidate keys

[frostming]

Fixes #2120

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-commenter]

Codecov Report

Patch coverage: 100.00% and no project coverage change.

Comparison is base (279edb4) 84.45% compared to head (f61418e) 84.45%.

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Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2123   +/-   ##
=======================================
  Coverage   84.45%   84.45%           
=======================================
  Files         100      100           
  Lines        9711     9713    +2     
  Branches     2135     2136    +1     
=======================================
+ Hits         8201     8203    +2     
  Misses       1044     1044           
  Partials      466      466           

Flag	Coverage Δ
unittests	84.22% <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/models/repositories.py	72.25% <100.00%> (-0.09%)	⬇️
src/pdm/resolver/providers.py	92.71% <100.00%> (+0.14%)	⬆️

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[apoorvkh]

@frostming Would you consider creating a minor version release that includes this fix? Thank you!