Generate separate project and group work items fixtures

What does this MR do and why?

Fix test fixtures

spec/frontend/fixtures/work_items.rb and ee/spec/frontend/fixtures/work_items.rb generate text fixtures to the same file graphql/work_items/namespace_work_item_types.query.graphql.json. This appears to cause a race condition on the CI pipelines which causes jest tests to non-deterministically use one output or another

References

• Fix #537479 (closed).
• gitlab-org/quality/engineering-productivity/master-broken-incidents#12365 (closed)

Screenshots or screen recordings

How to set up and validate locally

MR acceptance checklist

Evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.