Patch release 2.8.6

[robinmolen]

Partly closes #5126

Changes

Patch release for 2.8.6. Updated backend translations and changelog, and bumped version.

Checklist

Check off the items that are completed or not relevant.

• Impact on features

  • Checked copying a form
  • Checked import/export of a form
  • Config checks in the configuration overview admin page
  • Problem detection in the admin email digest is handled

• Release management

  • I have labelled the PR as "needs-backport" accordingly

• I have updated the translations assets (you do NOT need to provide translations)

  • Ran ./bin/makemessages_js.sh
  • Ran ./bin/compilemessages_js.sh

• Dockerfile/scripts

  • Updated the Dockerfile with the necessary scripts from the ./bin folder

• Commit hygiene

  • Commit messages refer to the relevant Github issue
  • Commit messages explain the "why" of change, not the how

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 96.57%. Comparing base (466ad0e) to head (074f325).
Report is 3 commits behind head on stable/2.8.x.

Additional details and impacted files

@@              Coverage Diff              @@
##           stable/2.8.x    #5129   +/-   ##
=============================================
  Coverage         96.57%   96.57%           
=============================================
  Files               747      747           
  Lines             25337    25337           
  Branches           3344     3344           
=============================================
  Hits              24469    24469           
  Misses              603      603           
  Partials            265      265           

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