Switch to Trusted Publishing for package upload to PyPI in CI

Trusted publishing (with attestations) is currently suggested as good practice to ensure confidence that what users download from PyPI is the same artifact that was generated in GitHub CI, meaning that what I see in GitHub is the same as what is installed - handy for auditing. It also avoids the presence of PyPI tokens as 'secrets' in the CI, which can be exfiltrated by bad actors.

Following the recent litellm supply chain attack this week, I would like to express my support for this^*. The uvloop package is one of 16 packages in the top 500 PyPI packages (by downloads) which use the pypa/gh-action-pypi-publish action but have not yet upgraded it to use Trusted Publishing: this is 'low hanging fruit' in terms of making Python a more secure programming environment.

Instead of using the stored secret token, GitHub vouches for the upload, and PyPI checks the uploading CI workflow filename against a pre-declared filename you set ahead of time (in uvloop's case the filename is release.yml). It also requires creating an 'environment' for the repo on GitHub (suggested name "pypi") which you also register the package with on PyPI.

^* Post-mortems of the litellm attack:

1. https://futuresearch.ai/blog/litellm-pypi-supply-chain-attack/
2. https://snyk.io/articles/poisoned-security-scanner-backdooring-litellm/

從 .github/workflows/release.yml 開始，檢查 publish job，尤其是其中的 Upload to PyPI 步驟。設定 GitHub environment 和對應的 PyPI registration，接著更新 job permissions 並移除 password argument。當 releases 使用帶有 attestations 的 Trusted Publishing，而不是 PyPI token 時，就表示完成。