chore(deps): bump slackapi/slack-github-action from 1.26.0 to 2.1.1

Bumps [slackapi/slack-github-action](https://github.com/slackapi/slack-github-action) from 1.26.0 to 2.1.1.
- [Release notes](https://github.com/slackapi/slack-github-action/releases)
- [Commits](https://github.com/slackapi/slack-github-action/compare/70cd7be8e40a46e8b0eced40b0de447bdb42f68e...91efab103c0de0a537f72a35f6b8cda0ee76bf0a)

---
updated-dependencies:
- dependency-name: slackapi/slack-github-action
  dependency-version: 2.1.1
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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