Add accessibility assertions for artifact registry settings

What does this MR do and why?

Add accessibility assertions for artifact registry settings

Fix accessibility errors empty-heading & heading-order

Addresses errors with tests:

1) empty-heading: Headings should not be empty (minor)
    https://dequeuniversity.com/rules/axe/4.8/empty-heading?application=axeAPI
    The following 1 node violate this rule:
    
        Selector: h4
        HTML: <h4 class="gl-mt-0"><!----></h4>
        Fix any of the following:
        - Element does not have text that is visible to screen readers
        - aria-label attribute does not exist or is empty
        - aria-labelledby attribute does not exist, references elements that do not exist or references elements that are empty
        - Element has no title attribute
        
2) heading-order: Heading levels should only increase by one (moderate)
    https://dequeuniversity.com/rules/axe/4.8/heading-order?application=axeAPI
    The following 1 node violate this rule:
    
        Selector: h4
        HTML: <h4 class="gl-mt-0"><!----></h4>
        Fix any of the following:
        - Heading order invalid

Closes #462970 (closed)

MR acceptance checklist

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Screenshots or screen recordings

No change.

How to set up and validate locally

1. Visit Settings > Integrations for project & group.
2. Check any integration to confirm there is no change in UI
3. Additionally run tests in ee/spec/features/projects/integrations/google_cloud_platform/user_activates_artifact_registry_spec.rb

Validate Google Artifact Registry settings locally

1. Simulate a SAAS instance in local GDK

2. In rails console enable the experiment

   Feature.enable(:google_cloud_support_feature_flag)

3. Visit Project > Settings > Integrations > Google Cloud IAM and complete the fields with random values.

4. Visit Project > Settings > Integrations > Google Artifact Registry & confirm there is no change in UI