ci: migrate to GitHub Actions from CircleCI, allow running Browserstack on forked repo via label

[ylemkimon]

From #2415:

Pros:

• Nice integration with GitHub
• Single codebase/infrastructure
• Able to test on MacOS and Windows
• Easier to view results
• Annotation support
• Doesn't have problem with forked repo enabling CI

Cons:

• Not possible to reuse steps. The amount of code duplication is a bit high (Next Steps for Fully Functioning Composite Actions actions/runner#646)
• Harder to view artifacts, e.g., screenshot diffs and new screenshots. They are zipped and have to be downloaded
• Cannot skip if code is not changed, with required status checks enabled (but they only take <2 min. and GitHub Actions hour is unlimited)
• [ci skip] or [skip ci] doesn't work for pull requests

• Disable CircleCI
• Disable Screenshotter bot
• Remove Screenshotter bot GitHub App
• Remove CircleCI from required status checks
• Add GitHub Actions to required status checks
• Update other pull requests

[kevinbarabash]

That was fast. Thanks for moving us over to GitHub Actions.

[kevinbarabash]

Why did the coverage report change so drastically? I wouldn't expect any change in those numbers from this PR.

[ylemkimon]

It seems the codecov-action is uploading coverage/coverage-final.json, which was not uploaded with codecov-node. This file seems to have different method of counting lines, so coverage seems to have changed.

[kevinbarabash]

@ylemkimon do you need my help with any of the checkbox items at the top?

[ylemkimon]

@kevinbarabash No, they are to-dos after this PR is merged.

[kevinbarabash]

In that case I better review this. 🙂

[kevinbarabash]

Thanks for migrating CircleCI stuff to GitHub Actions. It'll be nice to have all of the CI workflows using the same system. Was #2418 a test for this PR? If so, wouldn't the base of that PR need to be the head of this one? I think it would be good to also do a PR from a fork to test that flow. Also, more comments especially for some of the if statements in the ci.yml will be helpful if other people need to look at the file in the future.

[kevinbarabash]

This docs for this action say that it's possible to require external scripts. If we did that we could lint the script.

[ylemkimon]

@kevinbarabash The repo has to be checked out in order to run the script on the repo. However, this job doesn't check out the repo, and adding checkout will increase the time by about 5 seconds, where this job takes only 1-2 seconds.

[kevinbarabash]

I didn't realize that. That's good to know.

[ylemkimon]

@kevinbarabash I'm creating a ESLint plugin, which lints JavaScript in GitHub Actions workflow. I'll enable it later.

[kevinbarabash]

LGTM. There are a couple of more places in ci.yml that could use comments before merging this, see inline comments for details.

[ylemkimon]

@kevinbarabash Thank you for the review! I've confirmed they work as intended in #2429. Could you stop CircleCI builds in https://app.circleci.com/settings/project/github/KaTeX/KaTeX?

[kevinbarabash]

I've stopped the CircleCI builds.

[edemaine]

Exciting! Nice work.