Offer Python Latest (nightly master trunk build)

One of the features I love most about TravisCI is the ability to build my projects CI with top of Trunk Python (master branch). This allows me to know about deprecations etc. coming very early and have time to work on the fixes sooner.

Can actions look at supporting building a Trunk version nightly? Here is an example usage with Travis: https://github.com/facebookincubator/ptr/blob/master/.travis.yml#L16

Haven't dug in deep, but would also love to have the ability for this build to be able to fail and not flag CI failure, like the Travis config above does.

Thanks.

この Issue では setup-python のファイルやテストは指定されていません。まず setup-python リポジトリのエントリーポイントと、facebookincubator/ptr にあるリンク先の Travis 設定を確認し、nightly Python master build と、失敗を許容する場合の挙動を理解してください。workflows から nightly trunk build を要求でき、想定された失敗によって CI 全体が失敗にならなければ完了です。