Bump slack-sdk from 3.23.1 to 3.26.1

Bumps [slack-sdk](https://github.com/slackapi/python-slack-sdk) from 3.23.1 to 3.26.1.
- [Release notes](https://github.com/slackapi/python-slack-sdk/releases)
- [Changelog](https://github.com/slackapi/python-slack-sdk/blob/main/docs-v2/changelog.html)
- [Commits](slackapi/python-slack-sdk@v3.23.1...v3.26.1)

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

Signed-off-by: dependabot[bot] <support@github.com>

requirements.txt

@@ -48,7 +48,7 @@ qrcode==7.4.2
 requests==2.31.0
 service-identity==23.1.0
 six==1.16.0
-slack-sdk==3.23.1
+slack-sdk==3.26.1
 sqlparse==0.4.4
 stripe==7.4.0
 Twisted==23.10.0