Sign GitHub releases

[afuetterer]

Refs:

• https://python-semantic-release.readthedocs.io/en/latest/github-action.html
• https://python-semantic-release.readthedocs.io/en/latest/github-action.html#ssh-public-signing-key
• https://github.com/sigstore/sigstore-python
• https://github.com/sigstore/gh-action-sigstore-python
• https://github.com/search?q=%22uses%3A+sigstore%2Fgh-action-sigstore-python%22+language%3AYAML&type=code&l=YAML

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[github-actions]

This issue is stale because it has been open 60 days without activity.
Remove 'abandoned' label or comment or this will be closed in 7 days.

[github-actions]

This issue was closed because it has been stalled for 7 days with no activity.

[github-actions]

This issue is stale because it has been open 90 days without activity.
Remove 'abandoned' label or comment or this will be closed in 14 days.