Merge branch 'fix-groups-helper-spec' into 'master'

Always use `fixture_file_upload` helper to upload files in tests.

## What does this MR do?

Fix a broken spec.

## Are there points in the code the reviewer needs to double check?

## Why was this MR needed?

## Screenshots (if relevant)

## Does this MR meet the acceptance criteria?

- [ ] [Changelog entry](https://docs.gitlab.com/ce/development/changelog.html) added
- [ ] [Documentation created/updated](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/doc_styleguide.md)
- [ ] API support added
- Tests
  - [ ] Added for this feature/bug
  - [ ] All builds are passing
- [ ] Conform by the [merge request performance guides](http://docs.gitlab.com/ce/development/merge_request_performance_guidelines.html)
- [ ] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [ ] Branch has no merge conflicts with `master` (if it does - rebase it please)
- [ ] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

## What are the relevant issue numbers?

See merge request !8164

spec/helpers/groups_helper_spec.rb

@@ -6,7 +6,7 @@ describe GroupsHelper do
 
     it 'returns an url for the avatar' do
       group = create(:group)
-      group.avatar = File.open(avatar_file_path)
+      group.avatar = fixture_file_upload(avatar_file_path)
       group.save!
       expect(group_icon(group.path).to_s).
         to match("/uploads/group/avatar/#{group.id}/banana_sample.gif")