chore: allow missing docs in tests

[SimonThormeyer]

After upgrading to Rust 1.83, this rule is enforced in a different way, which requires us to change it for tests.

What's new in this PR

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PR Submission Checklist for internal contributors

• The PR Title
  • conforms to the style of semantic commits messages¹ supported in Wire's Github Workflow²
  • contains a reference JIRA issue number like SQPIT-764
  • answers the question: If merged, this PR will: ... ³

1. https://sparkbox.com/foundry/semantic_commit_messages
2. https://github.com/wireapp/.github#usage
3. E.g. feat(conversation-list): Sort conversations by most emojis in the title #SQPIT-764.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 80.03%. Comparing base (5870dec) to head (27a05d0).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #277   +/-   ##
=======================================
  Coverage   80.03%   80.03%           
=======================================
  Files          49       49           
  Lines        4323     4323           
=======================================
  Hits         3460     3460           
  Misses        863      863