Use `GlModal` in `_protected_branch.html.haml`

app/views/projects/protected_branches/shared/_protected_branch.html.haml

@@ -20,4 +20,4 @@
 
   - if can_admin_project
     %td
-      = link_to s_('ProtectedBranch|Unprotect'), [@project, protected_branch, { update_section: 'js-protected-branches-settings' }], disabled: local_assigns[:disabled], data: { confirm: s_('ProtectedBranch|Branch will be writable for developers. Are you sure?') }, method: :delete, class: "btn gl-button btn-warning"
+      = link_to s_('ProtectedBranch|Unprotect'), [@project, protected_branch, { update_section: 'js-protected-branches-settings' }], disabled: local_assigns[:disabled], aria: { label: s_('ProtectedBranch|Unprotect branch') }, data: { confirm: s_('ProtectedBranch|Branch will be writable for developers. Are you sure?'), confirm_btn_variant: 'danger' }, method: :delete, class: "btn gl-button btn-warning"

locale/gitlab.pot

@@ -29286,6 +29286,9 @@ msgstr ""
 msgid "ProtectedBranch|Unprotect"
 msgstr ""
 
+msgid "ProtectedBranch|Unprotect branch"
+msgstr ""
+
 msgid "ProtectedBranch|What are protected branches?"
 msgstr ""