fix: No unlock button for published content, edit preview button for locked versions

[fsbraun]

Description

This PR resolves a problem where the unlock button on a published version (where unlocking does not make sense).

It also adds a preview button to a locked version in the version change list.

Related resources

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Checklist

• I have opened this pull request against master
• I have added or modified the tests when changing logic
• I have followed the conventional commits guidelines to add meaningful information into the changelog
• I have read the contribution guidelines and I have joined #workgroup-pr-review on
  Slack to find a “pr review buddy” who is going to review my pull request.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 90.88%. Comparing base (f90c5b2) to head (7fb4aa0).
Report is 4 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #365   +/-   ##
=======================================
  Coverage   90.88%   90.88%           
=======================================
  Files          72       72           
  Lines        2546     2546           
  Branches      361      361           
=======================================
  Hits         2314     2314           
  Misses        168      168           
  Partials       64       64           

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