fix: don't install a local file if it doesn't change

[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 0% with 1 line in your changes missing coverage. Please review.

Project coverage is 85.30%. Comparing base (03b3114) to head (d18aad0).

Files	Patch %	Lines
src/pdm/installers/synchronizers.py	0.00%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2966   +/-   ##
=======================================
  Coverage   85.30%   85.30%           
=======================================
  Files         106      106           
  Lines       10697    10697           
  Branches     2337     2337           
=======================================
  Hits         9125     9125           
  Misses       1094     1094           
  Partials      478      478           

Flag	Coverage Δ
unittests	85.07% <0.00%> (ø)

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