Update version text and add stage metadata

Fixes one version text line, and adds missing
stage metadata to related files in the same dir

doc/user/project/merge_requests/accessibility_testing.md

 ---
+stage: Verify
+group: Testing
+info: To determine the technical writer assigned to the Stage/Group associated with this page, see https://about.gitlab.com/handbook/engineering/ux/technical-writing/#designated-technical-writers
 type: reference, howto
 ---
 
@@ -20,7 +23,9 @@ analyzed to a file called `accessibility`.
 
 ## Accessibility Merge Request widget
 
-[Since GitLab 13.0](https://gitlab.com/gitlab-org/gitlab/-/issues/39425), in addition to the report artifact that is created, GitLab will also show the
+> [Introduced](https://gitlab.com/gitlab-org/gitlab/-/issues/39425) in GitLab 13.0.
+
+In addition to the report artifact that is created, GitLab will also show the
 Accessibility Report in the merge request widget area:
 
 ![Accessibility Merge Request Widget](img/accessibility_mr_widget_v13_0.png)

doc/user/project/merge_requests/browser_performance_testing.md

 ---
+stage: Verify
+group: Testing
+info: To determine the technical writer assigned to the Stage/Group associated with this page, see https://about.gitlab.com/handbook/engineering/ux/technical-writing/#designated-technical-writers
 type: reference, howto
 ---
 

doc/user/project/merge_requests/code_quality.md

 ---
+stage: Verify
+group: Testing
+info: To determine the technical writer assigned to the Stage/Group associated with this page, see https://about.gitlab.com/handbook/engineering/ux/technical-writing/#designated-technical-writers
 type: reference, howto
 ---
 

doc/user/project/merge_requests/fail_fast_testing.md

 ---
+stage: Verify
+group: Testing
+info: To determine the technical writer assigned to the Stage/Group associated with this page, see https://about.gitlab.com/handbook/engineering/ux/technical-writing/#designated-technical-writers
 type: reference, howto
 ---
 

doc/user/project/merge_requests/test_coverage_visualization.md

 ---
+stage: Verify
+group: Testing
+info: To determine the technical writer assigned to the Stage/Group associated with this page, see https://about.gitlab.com/handbook/engineering/ux/technical-writing/#designated-technical-writers
 type: reference, howto
 ---
 

doc/user/project/merge_requests/testing_and_reports_in_merge_requests.md

 ---
+stage: Verify
+group: Testing
+info: To determine the technical writer assigned to the Stage/Group associated with this page, see https://about.gitlab.com/handbook/engineering/ux/technical-writing/#designated-technical-writers
 type: index
 description: "Test your code and display reports in merge requests"
 ---