[PR #11714/0d77d0d6 backport][3.13] Fix loading netrc when NETRC env var is not set

[patchback]

This is a backport of PR #11714 as merged into master (0d77d0d).

What do these changes do?

I optimized this one a bit too much assuming NETRC would always be set in #11634

fixes #11713

Are there changes in behavior for the user?

fix regression

Is it a substantial burden for the maintainers to support this?

no

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.25%. Comparing base (e6042d2) to head (5f7f41b).
⚠️ Report is 1 commits behind head on 3.13.
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@           Coverage Diff           @@
##             3.13   #11727   +/-   ##
=======================================
  Coverage   98.25%   98.25%           
=======================================
  Files         128      128           
  Lines       43825    43849   +24     
  Branches     2385     2385           
=======================================
+ Hits        43059    43083   +24     
  Misses        590      590           
  Partials      176      176           

Flag	Coverage Δ
CI-GHA	98.13% <100.00%> (+<0.01%)	⬆️
OS-Linux	97.89% <100.00%> (+<0.01%)	⬆️
OS-Windows	95.59% <100.00%> (+<0.01%)	⬆️
OS-macOS	97.12% <100.00%> (+<0.01%)	⬆️
Py-3.10.11	96.66% <100.00%> (+<0.01%)	⬆️
Py-3.10.18	97.16% <100.00%> (?)
Py-3.10.19	?
Py-3.11.13	97.35% <100.00%> (?)
Py-3.11.14	?
Py-3.11.9	96.85% <100.00%> (+<0.01%)	⬆️
Py-3.12.10	96.94% <100.00%> (+<0.01%)	⬆️
Py-3.12.11	97.44% <100.00%> (?)
Py-3.12.12	?
Py-3.13.7	97.45% <100.00%> (?)
Py-3.13.8	?
Py-3.13.9	96.92% <100.00%> (?)
Py-3.14.0	97.66% <100.00%> (+<0.01%)	⬆️
Py-3.14.0t	96.74% <100.00%> (+<0.01%)	⬆️
Py-3.9.13	96.56% <100.00%> (+<0.01%)	⬆️
Py-3.9.23	97.06% <100.00%> (?)
Py-3.9.24	?
Py-pypy3.9.19-7.3.16	88.57% <100.00%> (+1.10%)	⬆️
VM-macos	97.12% <100.00%> (+<0.01%)	⬆️
VM-ubuntu	97.89% <100.00%> (+<0.01%)	⬆️
VM-windows	95.59% <100.00%> (+<0.01%)	⬆️

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[codspeed-hq]

CodSpeed Performance Report

Merging #11727 will not alter performance

_{Comparing patchback/backports/3.13/0d77d0d64461bd9c98b30fb1f5ab246bb58f2b4e/pr-11714 (5f7f41b) with 3.13 (e6042d2)}

Summary

✅ 59 untouched