Follow-up from "Bugfix: add route to coverage_fuzzing_reports"

The following discussion from !43664 (merged) should be addressed:

• @dzaporozhets started a discussion: (+1 comment)

  We do author: create(:user) for each report in this file. How about we make it let_it_be on top of the file and reuse it? Candidate for a follow-up merge request.