Fix formatting of PR ping Slack messages

[krysal]

Fixes

Follow up #3577 and #3651

Description

Last notification of new PR received has bad formatting.

This is a quick PR to fix it, removing leftovers of when the action used curl calls.

Checklist

• My pull request has a descriptive title (not a vague title likeUpdate index.md).
• My pull request targets the default branch of the repository (main) or a parent feature branch.
• My commit messages follow best practices.
• My code follows the established code style of the repository.
• I added or updated tests for the changes I made (if applicable).
• I added or updated documentation (if applicable).
• I tried running the project locally and verified that there are no visible errors.
• I ran the DAG documentation generator (if applicable).

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[sarayourfriend]

The PR limit reminders job is also failing. I'll look into it now.

Fix for that here: #3657

[dhruvkb]

Some spaces between the words are missing, except that it LGTM!