Allow Test PyPI publish to skip existing versions

On pushes to main the version may not have been bumped, so the
upload would fail with 400. Use skip-existing to handle this
gracefully.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: jensens

.github/workflows/release.yml

@@ -120,6 +120,7 @@ jobs:
         uses: pypa/gh-action-pypi-publish@release/v1
         with:
           repository-url: https://test.pypi.org/legacy/
+          skip-existing: true
 
   # Upload to real PyPI on GitHub Release
   release-pypi: