Switch to Trusted Publishing for package upload to PyPI in CI

Personne n'a encore pris cette issue.

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](https://hugovk.github.io/top-pypi-packages/)) 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/

Implementation (click to expand)

* Configure (or use an existing) GitHub environment, and register with PyPI

* Add the [environment definition](https://docs.github.com/en/actions/reference/workflows-and-actions/workflow-syntax#jobsjob_idenvironment) to the same `publish` job

* Add `id-token: write`, `contents: write` and `packages: write` [permissions](https://docs.github.com/en/actions/reference/workflows-and-actions/workflow-syntax#jobsjob_idpermissions) to the same `publish` job

* specifying any permission restricts the token, and creating a GitHub release requires `contents: write` and potentially `packages: write`

* Remove `password` argument in the `Upload to PyPI` step of the `publish` job of the [Build & Publish](https://github.com/MagicStack/uvloop/blob/master/.github/workflows/release.yml) CI workflow

* Optionally remove the `PYPI_TOKEN` project secret

Commencez par .github/workflows/release.yml et examinez le job publish, en particulier son étape Upload to PyPI. Configurez l’environnement GitHub et l’enregistrement PyPI correspondant, puis mettez à jour les permissions du job et supprimez l’argument de mot de passe. La tâche est terminée lorsque les releases utilisent Trusted Publishing avec des attestations au lieu d’un token PyPI.

Rédigé par le modèle d'indexation à partir du texte de l'issue.