ci: bump slackapi/slack-github-action from 1.27 to 2.0

Bumps [slackapi/slack-github-action](https://github.com/slackapi/slack-github-action) from 1.27 to 2.0.
- [Release notes](https://github.com/slackapi/slack-github-action/releases)
- [Commits](slackapi/slack-github-action@v1.27...v2.0)

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

Signed-off-by: dependabot[bot] <[email protected]>

.github/workflows/draft-pr-converter.yml

@@ -77,7 +77,7 @@ jobs:
       - name: Post to a Slack channel
         id: slack
         if: ${{ steps.mutation_step.outputs.exec == 'true' }}
-        uses: slackapi/slack-github-action@v1.27
+        uses: slackapi/slack-github-action@v2.0
         with:
           channel-id: 'C02LMULF4NA'
           payload: '{ "type": "mrkdwn", "text": "${{ env.SLACK_MESSAGE }}" }'