Bump slackapi/slack-github-action from 2.0.0 to 2.1.0 (#71)

Bumps [slackapi/slack-github-action](https://github.com/slackapi/slack-github-action) from 2.0.0 to 2.1.0.
- [Release notes](https://github.com/slackapi/slack-github-action/releases)
- [Commits](slackapi/slack-github-action@v2.0.0...v2.1.0)

---
updated-dependencies:
- dependency-name: slackapi/slack-github-action
  dependency-version: 2.1.0
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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