Refactor: move shared_examples to ee
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The following discussion from !44097 should be addressed:
- [ ] @reprazent started a [discussion](https://gitlab.com/gitlab-org/gitlab/-/merge_requests/44097#note_423512926): (+2 comments)
> Should this shared example live in `ee/spec/support/shared_examples/` ?
- [ ] @reprazent started a [discussion](https://gitlab.com/gitlab-org/gitlab/-/merge_requests/44097#note_424377322): (+2 comments)
> I would argue that the `multiple assignees merge request` shared examples also live in the wrong place, as they're only used in EE:
```
File: spec/support/shared_examples/features/multiple_assignees_mr_shared_examples.rb
3:24:RSpec.shared_examples 'multiple assignees merge request' do |action, save_button_title|
File: ee/spec/features/merge_request/user_creates_multiple_assignees_mr_spec.rb
12:20: it_behaves_like 'multiple assignees merge request', 'creates', 'Submit merge request'
File: ee/spec/features/merge_request/user_edits_multiple_assignees_mr_spec.rb
12:20: it_behaves_like 'multiple assignees merge request', 'updates', 'Save changes'
```
> That said, I'm okay with moving them all together in a separate MR that has `[RUN AS-IF-FOSS]` in the title to make sure.
issue