Update slack-sdk requirement in /src/weekly-post

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)
- [Commits](https://github.com/slackapi/python-slack-sdk/compare/v3.42.0...v3.43.0)

---
updated-dependencies:
- dependency-name: slack-sdk
  dependency-version: 3.43.0
  dependency-type: direct:production
...

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

src/weekly-post/requirements.txt

@@ -1,2 +1,2 @@
-slack_sdk>=3.42.0,<4.0
+slack_sdk>=3.43.0,<4.0
 boto3>=1.43.38