build(deps): bump slack-bolt from 1.27.0 to 1.28.0 (#77)

Bumps [slack-bolt](https://github.com/slackapi/bolt-python) from 1.27.0 to 1.28.0.
- [Release notes](https://github.com/slackapi/bolt-python/releases)
- [Commits](slackapi/bolt-python@v1.27.0...v1.28.0)

---
updated-dependencies:
- dependency-name: slack-bolt
  dependency-version: 1.28.0
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

Author: dependabot[bot]

requirements.txt

@@ -1,3 +1,3 @@
 pytest==9.0.2
 ruff==0.15.8
-slack-bolt==1.27.0
+slack-bolt==1.28.0