Removed pinned django-treebeard

[tidenhub]

Description

This change removes an old issue protecting broken changes in django-treebeard 4.5.0 where the core CMS and treebeard has since received patches.

Related resources

• Issue introduced in 4.5: https://github.com/django-treebeard/django-treebeard/blob/master/CHANGES.md#release-45-feb-17-2021
• Resolved in 4.5.1: https://github.com/django-treebeard/django-treebeard/blob/master/CHANGES.md#release-451-feb-22-2021

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

Merging #59 (472d904) into master (029016e) will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##            master       #59   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           10        10           
  Lines          143       143           
  Branches        34        25    -9     
=========================================
  Hits           143       143           

[fsbraun]

@tidenhub thank you so much for this PR. Can you please add an entry into the change log? Thank you so much.

[tidenhub]

@fsbraun Done.