[TM-280] Fix changelog

Description

Problem: recent changes from TM-280 appeared in 0.6.0 changes by mistake (artifact of conflict-less rebase), they in fact were applied after 0.6.0 release.

Solution: move the corresponding section to Unreleased.

To avoid such mistakes next time, I recommend inserting new entries in the beginning of the changes list, and also leave no blank line after version header - now if s/Unreleased/v1.2.3 change and addition of new changelog entry are committed in parallel, someone will encounter a rebase conflict.

Related issue(s)

Resolves #

✅ Checklist for your Merge Request

Related changes (conditional)

• Tests (see short guidelines)

  • If I added new functionality, I added tests covering it.
  • If I fixed a bug, I added a regression test to prevent the bug from silently reappearing again.

• Documentation

  • I checked whether I should update the docs and did so if necessary:
    • README
    • Haddock
    • docs/
  • I updated the changelog if my changes are externally visible.

Stylistic guide (mandatory)

• My commits comply with the following policy.
• My code complies with the style guide.