fix(ci): switch release trigger to push on main for PyPI environment compatibility

[eschaar]

Summary

Release workflow and test isolation fixes for PyPI publishing.

• Fixed release workflow trigger: switched from pull_request: closed to push: branches: [main] so the workflow runs under refs/heads/main and satisfies the PyPI environment deployment branch protection rule.
• Fixed build job checkout missing fetch-depth: 0, required by poetry-dynamic-versioning to read git tags.
• Fixed download-artifact version mismatch (v5 → v7) to align with upload-artifact@v7.
• Simplified release workflow job names: release, build, publish.
• Updated CHANGELOG with 1.3.1 and corrected 1.3.0 entries.

Related Issues

N/A

Validation

• Tests pass locally
• CI checks pass
• Docs updated (if needed)

Release Impact

• fix: (patch) — workflow and artifact version fixes

[Copilot]

Pull request overview

Adjusts the GitHub Actions release workflow so PyPI publishing can run under refs/heads/main (compatible with protected PyPI environments), and updates the changelog accordingly.

Changes:

• Switched the release workflow trigger from pull_request: closed to push on main and removed PR-only guards/checkout refs.
• Ensured release/build/publish jobs are gated only by the computed “version changed” output and aligned artifact action versions.
• Added a 1.3.1 changelog entry and amended 1.3.0 with a “Fixed” section.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
CHANGELOG.md	Adds 1.3.1 notes and amends 1.3.0, describing workflow/test-related fixes.
.github/workflows/release.yml	Updates workflow trigger and job conditions to run releases from main pushes and publish via the protected PyPI environment.