ENH: Trigger PR labeler workflows from forks

[jhlegarreta]

Change the GitHub webhook event to a pull_request_target event to
trigger the PR labeler workflows from forks.

See documentation:
https://docs.github.com/en/actions/reference/events-that-trigger-workflows#pull_request_target
and
https://github.blog/2020-08-03-github-actions-improvements-for-fork-and-pull-request-workflows/

PR Checklist

• No API changes were made (or the changes have been approved)
• No major design changes were made (or the changes have been approved)

[jhlegarreta]

Let's see if this makes the trick.

If the events are triggered too frequently, once that is verified, we may want to restrict them to the [opened, edited] types in a future PR.

[dzenanz]

It would be a great improvement if it worked.

[dzenanz]

If this works, will it allows us to also apply clang-format on PRs from forks?

[jhlegarreta]

If this works, will it allows us to also apply clang-format on PRs from forks?

Not 100% sure how the commands throughout the comments on a PR work, but chances are that it might.

Edit: not sure if the current clang-format command is triggered using the kwrobot-1 actions, but this action seems to have the ability to trigger such processes.

[jhlegarreta]

😭 The Actions failed:
https://github.com/InsightSoftwareConsortium/ITK/runs/2188115680?check_suite_focus=true

The webhook event is not supported yet:
srvaroa/labeler#13

😔.

[dzenanz]

Should we revert this PR?

[jhlegarreta]

Should we revert this PR?

Not sure; the workflow does not show the error in the PR/marks the check as passing, and hence it will not be considered as an unsuccessful check when merging the PRs (somewhat similar to what it was before).

Maybe we could track it as an issue? But even then, we purely depend on the author of the labeler action or someone else (I think I might not have the bandwidth to learn go and to try at this time) contributing provided that the feature gets merged into a release in google's go-github repository.

We could ask to the google folks if they will merge it, or propose the labeler action repo owner to switch to track the go-github master branch (the latter being probably not desired).

Edit: another option is to use other labeler actions; I have not found any doing both tasks (labeling according to the PR title and the changed files), but there are some that do one or the other, so we would have two workflows.