Check Changelog: Listen to labeled and unlabeled events (#1151)
Check Changelog: Listen to labeled and unlabeled events (#1151)

Adding and removing labels doesn't trigger an `edited` event, so
previously the check would not be skipped when the `c: dependencies`
label was added automatically shortly after Dependabot PRs were
opened.

https://docs.github.com/en/actions/reference/events-that-trigger-workflows#pull_request

Closes W-8737039.

[skip changelog]
AltSchool/heroku-buildpack-python,AltSchool/heroku-buildpack-python,Scalingo/python-buildpack,heroku/heroku-buildpack-python,Scalingo/python-buildpack,heroku/heroku-buildpack-python