Clean unnecessary 'attachToDocument' in 'ee/spec/frontend/environments_dashboard'

Summary

As described in &2419 (closed), we need to clean up our Jest tests from unnecessary attachToDocument usage

Risks

No risks

Involved specs

• ee/spec/frontend/environments_dashboard/components/environment_header_spec.js
• ee/spec/frontend/environments_dashboard/components/environment_spec.js
• ee/spec/frontend/environments_dashboard/components/project_header_spec.js