chore(deps): bump slackapi/slack-github-action from 3.0.4 to 4.0.0 (#5978)

Bumps [slackapi/slack-github-action](https://github.com/slackapi/slack-github-action) from 3.0.4 to 4.0.0.
- [Release notes](https://github.com/slackapi/slack-github-action/releases)
- [Changelog](https://github.com/slackapi/slack-github-action/blob/main/CHANGELOG.md)
- [Commits](slackapi/slack-github-action@v3.0.4...v4.0.0)

---
updated-dependencies:
- dependency-name: slackapi/slack-github-action
  dependency-version: 4.0.0
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

.github/workflows/image-deps-updater.yaml

@@ -114,7 +114,7 @@ jobs:
 
       - name: Slack Notification
         if: ${{ steps.cpr.outputs.pull-request-number }}
-        uses: slackapi/slack-github-action@v3.0.4
+        uses: slackapi/slack-github-action@v4.0.0
         with:
           webhook: ${{ secrets.KOTS_IMAGE_DEPS_SLACK_WEBHOOK }}
           webhook-type: webhook-trigger