[8.x](backport #42359) github-actions: fix slack inputs

[mergify]

Proposed commit message

#42293 introduced a breaking change.

However, we can use https://github.com/elastic/oblt-actions/tree/main/slack/send if we want to avoid maintaining the thrid-party version. With https://github.com/elastic/oblt-actions we aim to keep backward compatibility

Checklist

• My code follows the style guidelines of this project
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have made corresponding change to the default configuration files
• I have added tests that prove my fix is effective or that my feature works
• I have added an entry in CHANGELOG.next.asciidoc or CHANGELOG-developer.next.asciidoc.

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Author's Checklist

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---

This is an automatic backport of pull request #42359 done by [Mergify](https://mergify.com).

[mergify]

Cherry-pick of 1752115 has failed:

On branch mergify/bp/8.x/pr-42359
Your branch is up to date with 'origin/8.x'.

You are currently cherry-picking commit 175211509.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Changes to be committed:
	modified:   .github/workflows/bump-elastic-stack-snapshot.yml
	modified:   .github/workflows/bump-golang.yml
	modified:   .github/workflows/notify-stalled-snapshots.yml

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   .github/workflows/updatecli-compose.yml

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally

[botelastic]

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