Add workflow to verify the changelog snippets

[Garanas]

Description of the proposed changes

Continuation of #6137 and #6138 .

Adds a verify stage so that the format of the snippets are verified.

[Garanas]

It's interesting how one can keep running into this problem:

• https://stackoverflow.com/questions/40978921/how-to-add-chmod-permissions-to-file-in-git