Add actionlint (#62364)
Summary:
This adds a linter for our GitHub actions. When a GitHub Actions workflow has an invalid definition, GitHub doesn't queue the job and doesn't report it as failed, so these can be hard to detect with the usual tools. This adds an explicit job to check if our workflow YAMLs are valid using [https://github.com/rhysd/actionlint](https://github.com/rhysd/actionlint). We deployed a similar check in pytorch/test-infra [here](https://github.com/pytorch/test-infra/pull/89).
This PR enables the linter and fixes all the issues it complained about (it did already catch one bug where we were leaving `CIRCLE_BRANCH` blank when uploading binary size)
Pull Request resolved: https://github.com/pytorch/pytorch/pull/62364
Reviewed By: zhouzhuojie
Differential Revision: D29973928
Pulled By: driazati
fbshipit-source-id: 83b365e98fd6cbdcd75eeb44daf1be1c89056f8d
