Update slack-sdk requirement from <3.26.2,>=3.13.0 to >=3.13.0,<3.26.3

Updates the requirements on [slack-sdk](https://github.com/slackapi/python-slack-sdk) to permit the latest version.
- [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@v3.13.0...v3.26.2)

---
updated-dependencies:
- dependency-name: slack-sdk
  dependency-type: direct:production
...

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

requirements.txt

@@ -25,4 +25,4 @@ rest-social-auth>=6.0.0,<9.0
 six>=1.12.0,<2.0
 soupsieve>=1.9,<2.0
 SQLAlchemy>=1.3.2,<3.0
-slack_sdk>=3.13.0,<3.26.2
+slack_sdk>=3.13.0,<3.26.3