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[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

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

Additional details and impacted files

```diff @@ 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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