Add `project_policy` to `flayignore`

The `ProjectPolicy` is meant to be declarative in nature, and it isn't
necessarily a good idea to remove all duplication here. That level of
indirection would _hurt_ readability, rather than improve it.

.flayignore

@@ -3,3 +3,4 @@ lib/gitlab/sanitizers/svg/whitelist.rb
 lib/gitlab/diff/position_tracer.rb
 app/controllers/projects/approver_groups_controller.rb
 app/controllers/projects/approvers_controller.rb
+app/policies/project_policy.rb
\ No newline at end of file