Update archive/github-actions-slack action to v2.4.0

[mend-for-github-com[bot]]

This PR contains the following updates:

Package	Type	Update	Change
archive/github-actions-slack	action	minor	v2.3.2 -> v2.4.0

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Release Notes

archive/github-actions-slack

### [`v2.4.0`](https://togithub.com/archive/github-actions-slack/releases/v2.4.0) [Compare Source](https://togithub.com/archive/github-actions-slack/compare/v2.3.2...v2.4.0) ##### What's Changed - Same escaping on both post and update message, [https://github.com/archive/github-actions-slack/pull/42](https://togithub.com/archive/github-actions-slack/pull/42) - Update all dependencies to latest version, [https://github.com/archive/github-actions-slack/pull/41](https://togithub.com/archive/github-actions-slack/pull/41) - Clean-up on unit test, [https://github.com/archive/github-actions-slack/pull/40](https://togithub.com/archive/github-actions-slack/pull/40)

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