Fix broken spec/requests/api/projects_spec.rb

https://gitlab.com/gitlab-org/gitlab/-/merge_requests/79968 removed
`requirements_access_level` from `project_attributes.yml`, and
https://gitlab.com/gitlab-org/gitlab/-/merge_requests/80667 re-added
this attribute to fix to fix a broken FOSS spec.

However, https://gitlab.com/gitlab-org/gitlab/-/merge_requests/80667
broke master because the attribute is used in EE. We now conditionally
add `requirements_access_level` as an expected key in EE and omit this
in FOSS builds.

Relates to https://gitlab.com/gitlab-org/gitlab/-/issues/352764

spec/requests/api/project_attributes.yml

@@ -121,7 +121,6 @@ project_feature:
     - created_at
     - metrics_dashboard_access_level
     - project_id
-    - requirements_access_level
     - security_and_compliance_access_level
     - updated_at
   computed_attributes:

spec/requests/api/projects_spec.rb

@@ -2166,6 +2166,7 @@ RSpec.describe API::Projects do
             approvals_before_merge
             compliance_frameworks
             mirror
+            requirements_access_level
             requirements_enabled
             security_and_compliance_enabled
             issues_template