Bump slackclient from 2.9.3 to 2.9.4 (#1138)

Bumps [slackclient](https://github.com/slackapi/python-slack-sdk) from 2.9.3 to 2.9.4.
- [Release notes](https://github.com/slackapi/python-slack-sdk/releases)
- [Changelog](https://github.com/slackapi/python-slack-sdk/blob/main/docs-src-v2/changelog.rst)
- [Commits](slackapi/python-slack-sdk@v2.9.3...v2.9.4)

---
updated-dependencies:
- dependency-name: slackclient
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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

setup.py

@@ -35,7 +35,7 @@
           'python-pidfile==3.0.0',
           'pymongo==3.12.3',
           'tzlocal>=2.0,<4.1',
-          'slackclient==2.9.3',
+          'slackclient==2.9.4',
           'sqlparse==0.4.4',
           'psutil==5.9.5',
           'ujson==5.4.0',