fix windows build crash on generate_self_schema.py

[davidhewitt]

We have a crash when building artifacts on windows caused by #674.

It looks like #173 didn't apply for windows, but fortunately the regeneration of generate_self_schema.py was harmlessly using the main interpreter. After #674 the generation is now using the wrong interpreter.

This should fix properly by avoiding regeneration on Windows too.

[codecov-commenter]

Codecov Report

Merging #682 (e11edc0) into main (a85cd36) will not change coverage.
The diff coverage is n/a.

❗ Current head e11edc0 differs from pull request most recent head 6acc1ea. Consider uploading reports for the commit 6acc1ea to get more accurate results

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Additional details and impacted files

@@           Coverage Diff           @@
##             main     #682   +/-   ##
=======================================
  Coverage   93.72%   93.72%           
=======================================
  Files          99       99           
  Lines       13802    13802           
  Branches       25       25           
=======================================
  Hits        12936    12936           
  Misses        860      860           
  Partials        6        6           

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[codspeed-hq]

CodSpeed Performance Report

Merging #682 dh/fix-schema-build (6acc1ea) will not alter performances.

Summary

🔥 0 improvements
❌ 0 regressions
✅ 125 untouched benchmarks

🆕 0 new benchmarks
⁉️ 0 dropped benchmarks