Bump slack-sdk from 3.38.0 to 3.39.0 in /demos

Bumps [slack-sdk](https://github.com/slackapi/python-slack-sdk) from 3.38.0 to 3.39.0.
- [Release notes](https://github.com/slackapi/python-slack-sdk/releases)
- [Commits](slackapi/python-slack-sdk@v3.38.0...v3.39.0)

---
updated-dependencies:
- dependency-name: slack-sdk
  dependency-version: 3.39.0
  dependency-type: direct:development
  update-type: version-update:semver-minor
...

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

Author: dependabot[bot]

demos/moderator_bot/requirements-dev.txt

@@ -18,7 +18,7 @@ pyyaml==6.0.3
 scikit-learn==1.7.2
 scipy==1.16.3
 six==1.17.0
-slack_sdk==3.38.0
+slack_sdk==3.39.0
 urllib3==2.5.0
 yarl==1.22.0
 zipp==3.23.0