fix: Remove private GHA mechanisms (#545) · Nextdoor/kingpin@31060f9

ubuntu-latest pipelines will use ubuntu-24.04 soon. For more details, see https://github.com/actions/runner-images/issues/10636

"pull_request_target.opened" is not a known webhook name (https://developer.github.com/v3/activity/events/types/)

"pull_request_target.reopened" is not a known webhook name (https://developer.github.com/v3/activity/events/types/)

"pull_request_target.synchronize" is not a known webhook name (https://developer.github.com/v3/activity/events/types/)

"pull_request_target.edited" is not a known webhook name (https://developer.github.com/v3/activity/events/types/)

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