Allow non-admin users to delete review requests (#29057)

Fix #14459

The following users can add/remove review requests of a PR
- the poster of the PR
- the owner or collaborators of the repository
- members with read permission on the pull requests unit

models/fixtures/collaboration.yml

@@ -45,3 +45,9 @@
   repo_id: 22
   user_id: 18
   mode: 2 # write
+
+-
+  id: 9
+  repo_id: 60
+  user_id: 38
+  mode: 2 # write