fix: Don't fetch environments on Admin variables page

What does this MR do and why?

A request to fetch environments would be sent on the Admin variables page when the ci_variable_settings_graphql FF is disabled, but that doesn't make sense as we're not in a project context.

A system test started to fail recently because of an ambiguous match on alert boxes.

The fix is to only fetch environments if we're in a project's context.

Possibly related MRs are:

• !95624 (merged) (most likely this one)
• !89332 (merged)
• !94267 (merged)
• !98856 (merged)

Screenshots or screen recordings

Before

After

How to set up and validate locally

On master

1. Ensure the ci_variable_settings_graphql feature flag is disabled (Feature.disable('ci_variable_settings_graphql'))
2. Visit http://gdk.test:3000/admin/application_settings/ci_cd
3. Notice the There was an error fetching the environments information. alert, similar to #376761 (closed)
4. You can inspect the XHR requests and notice a 404 request to http://gdk.test:3000/api/v4/projects/undefined/environments

Alternatively, you can also just run bin/rspec './spec/features/admin_variables_spec.rb[1:1:1:10]', it should fail with the same error as #376761 (closed).

On this branch

1. Ensure the ci_variable_settings_graphql feature flag is disabled (Feature.disable('ci_variable_settings_graphql'))
2. Visit http://gdk.test:3000/admin/application_settings/ci_cd
3. Notice there's no There was an error fetching the environments information. alert
4. You can inspect the XHR requests and shouldn't see any one to http://gdk.test:3000/api/v4/projects/undefined/environments

Alternatively, you can also just run bin/rspec './spec/features/admin_variables_spec.rb[1:1:1:10]', it should pass.

MR acceptance checklist

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• I have evaluated the MR acceptance checklist for this MR.

Related to #376761 (closed)