Fix update changelog workflow and paste missing changelog item

[AlexVelezLl]

Description

Fix update changelog workflow

Changelog

• Description: Fixes update changelog workflow to avoid expecting a comment after the invisible comment <!-- [DO NOT REMOVE-USED BY GH ACTION] CHANGELOG START -->.
• Products impact: none.
• Addresses: -
• Components: -
• Breaking: -
• Impacts a11y: -
• Guidance: -

Steps to test

Tested in learningequality/test-actions#26

Testing checklist

• Contributor has fully tested the PR manually
• If there are any front-end changes, before/after screenshots are included
• Critical and brittle code paths are covered by unit tests
• The change is described in the changelog section above

Reviewer guidance

• Is the code clean and well-commented?
• Are there tests for this change?
• Are all UI components LTR and RTL compliant (if applicable)?
• Add other things to check for here

After review

• The changelog item has been pasted to the CHANGELOG.md

Comments

[MisRob]

Thanks for taking care of this @AlexVelezLl! All good.