Remove tabindex from navigation skip link

* Since it’s the first focusable item in the DOM it doesn’t need `tabindex`.
* The use of a positive `tabindex` isn’t recommended and can negatively impact focus management.

app/views/layouts/header/_default.html.haml

@@ -2,7 +2,7 @@
 - user_status_data = user_status_properties(current_user)
 
 %header.navbar.navbar-gitlab.navbar-expand-sm.js-navbar{ data: { qa_selector: 'navbar' } }
-  %a.sr-only.gl-accessibility{ href: "#content-body", tabindex: "1" } Skip to content
+  %a.gl-sr-only.gl-accessibility{ href: "#content-body" } Skip to content
   .container-fluid
     .header-content
       .title-container

changelogs/unreleased/323483-skip-link-remove-tabindex.yml

+---
+title: Remove tabindex on skip link that could negatively impact keyboard focus management
+  and order
+merge_request: 55756
+author:
+type: other