[PR #10961/5e68276c backport][3.12] fix example in socket_factory docs

[patchback]

This is a backport of PR #10961 as merged into master (5e68276).

What do these changes do?

fix example codes in custom socket creation section of client_advanced.rst

Are there changes in behavior for the user?

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

Related issue number

Checklist

• I think the code is well written
• Unit tests for the changes exist
• Documentation reflects the changes
• If you provide code modification, please add yourself to CONTRIBUTORS.txt
  • The format is <Name> <Surname>.
  • Please keep alphabetical order, the file is sorted by names.
• Add a new news fragment into the CHANGES/ folder

[codspeed-hq]

CodSpeed Performance Report

Merging #10967 will not alter performance

_{Comparing patchback/backports/3.12/5e68276ca359860e8943b98bb4d2f40da6f4157e/pr-10961 (b7ec7e6) with 3.12 (2c55e88)}

Summary

✅ 59 untouched benchmarks

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.16%. Comparing base (2c55e88) to head (b7ec7e6).
Report is 3 commits behind head on 3.12.

✅ All tests successful. No failed tests found.

Additional details and impacted files

@@           Coverage Diff           @@
##             3.12   #10967   +/-   ##
=======================================
  Coverage   98.16%   98.16%           
=======================================
  Files         130      130           
  Lines       39754    39754           
  Branches     2241     2241           
=======================================
  Hits        39025    39025           
  Misses        557      557           
  Partials      172      172           

Flag	Coverage Δ
CI-GHA	98.05% <ø> (ø)
OS-Linux	97.77% <ø> (ø)
OS-Windows	95.27% <ø> (+<0.01%)	⬆️
OS-macOS	96.94% <ø> (ø)
Py-3.10.11	96.84% <ø> (+<0.01%)	⬆️
Py-3.10.17	97.37% <ø> (-0.02%)	⬇️
Py-3.11.12	97.47% <ø> (-0.01%)	⬇️
Py-3.11.9	96.93% <ø> (ø)
Py-3.12.10	97.83% <ø> (ø)
Py-3.13.3	97.82% <ø> (ø)
Py-3.9.13	96.72% <ø> (ø)
Py-3.9.22	97.26% <ø> (ø)
Py-pypy7.3.16	80.33% <ø> (-9.58%)	⬇️
VM-macos	96.94% <ø> (ø)
VM-ubuntu	97.77% <ø> (ø)
VM-windows	95.27% <ø> (+<0.01%)	⬆️

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