feat: respect ca certs in env vars

[frostming]

Signed-off-by: Frost Ming [email protected]

Fix #3076

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 80.00000% with 2 lines in your changes missing coverage. Please review.

Project coverage is 85.68%. Comparing base (865fc62) to head (8ed7d95).
Report is 93 commits behind head on main.

Files with missing lines	Patch %	Lines
src/pdm/models/session.py	80.00%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3090   +/-   ##
=======================================
  Coverage   85.67%   85.68%           
=======================================
  Files         109      109           
  Lines       10958    10964    +6     
  Branches     2393     2394    +1     
=======================================
+ Hits         9388     9394    +6     
  Misses       1083     1083           
  Partials      487      487           

Flag	Coverage Δ
unittests	85.47% <80.00%> (+<0.01%)	⬆️

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