[reland] Add a ci/no-build label (#58778)
Summary:
Depends on https://github.com/pytorch/pytorch-probot/pull/22. Adds a new label called `ci/no-build` that disables the CircleCI `build` workflow on PRs. The current behavior should be the same in the absence of `ci/no-build`.
Specifically, after this PR lands, for anyone who isn't rebased onto the latest `master`, I believe this will happen:
- when they push to their PR, the CircleCI app triggers CI
- the `pytorch-probot` app sees that their PR doesn't have the `ci/no-build` tag, so it also triggers CI
- the latter should auto-cancel the former
After checking with https://github.com/pytorch/pytorch/issues/59087, it looks like this would cause the "errored" number to go up and then go down as Circle jobs are canceled (saying "Your CircleCI tests were canceled") and then restarted:
<img width="868" alt="Screen Shot 2021-05-27 at 12 39 20 PM" src="https://user-images.githubusercontent.com/8246041/119887123-9667b080-bee8-11eb-8acb-e1967899c9d5.png">
Pull Request resolved: https://github.com/pytorch/pytorch/pull/58778
Reviewed By: malfet
Differential Revision: D28995335
Pulled By: samestep
fbshipit-source-id: 8d7543b911e4bbbeef14639baf9d9108110b97c8
