Bump slack-morphism from 2.2.0 to 2.4.0

Bumps [slack-morphism](https://github.com/abdolence/slack-morphism-rust) from 2.2.0 to 2.4.0.
- [Release notes](https://github.com/abdolence/slack-morphism-rust/releases)
- [Commits](abdolence/slack-morphism-rust@v2.2.0...v2.4.0)

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

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