Limit repetitive headers in accessibility widget

Description

The following discussion from !78138 (merged) should be addressed:

• @gdoyle started a discussion: (+3 comments)

  New badges

  I was looking through our Figma and realized we didn't have any guidance of where the New badge would fit, nor if we still needed it. I investigated a bit and we can replace the badge with just plain text New that is bold (UI label bold, 14px, weight 700). We use the same format for the Metrics MR widget as well. Would it be possible to fix this in this MR or should I create a follow-up?

  

Additional information: We decided to replace the new badge with the header for every new error found. This means that the widget list could potentially get long, and there would be repetitive new headers.

Proposal

Create new headers, one New and one Fixed. List all new errors found under new and fixed under fixed.

Designs in design management

Implementation guide

• Add header properties to the other content sections just like this line https://gitlab.com/gitlab-org/gitlab/-/blob/master/app/assets/javascripts/vue_merge_request_widget/widgets/accessibility/index.vue#L114
• The headers should be named New for newErrors, Not fixed for existingErrors and Fixed for resolvedErrors, refer to the design for more details #350680[MRWidgetUpdates.png]
• Update specs in https://gitlab.com/gitlab-org/gitlab/-/blob/master/spec/frontend/vue_merge_request_widget/widgets/accessibility/index_spec.js to check for the new header titles