Slack notification actions use deprecated/unmaintained action `Ilshidur/action-slack`

[niooss-ledger]

Hello,
This repository provides Slack notification actions which rely on Ilshidur/action-slack:

actions/slack/release/action.yml

Lines 133 to 134 in 1cec2f2

	- name: Send Slack notification
	uses: Ilshidur/action-slack@2.1.0

actions/slack-notification/action.yml

Lines 58 to 59 in 1cec2f2

	- name: Notify Slack
	uses: Ilshidur/action-slack@2.1.0

But https://github.com/Ilshidur/action-slack was archived on Jan 5. 2024, after a notice on Ilshidur/action-slack#255 :

Concerning what's coming next for this project, I consider stopping its maintenance, or at least deprecating it.
As Slack released it's official GitHub Action, I don't find any interest over maintaining an unofficial alternative, because I believe that the personal time I would commit to a project I don't use anymore will not be worth enough against the work of the Slack developers. I highly support open source and I believe that the official Action is the project to pursue. I don't plan to work on this project anymore.

I believe we should migrate to Slack Send GitHub Action (https://github.com/slackapi/slack-github-action).