Merge branch 'patch-236' into 'master'

Apply GitLab UI button styles to buttons in ee/app/views/projects/settings/slacks directory

See merge request gitlab-org/gitlab!42657

ee/app/views/projects/settings/slacks/edit.html.haml

@@ -15,9 +15,9 @@
           = form.text_field :alias, class: 'form-control', placeholder: @slack_integration.alias, required: true
 
       .footer-block.row-content-block
-        %button.btn.btn-success{ type: 'submit' }
+        %button.btn.gl-button.btn-success{ type: 'submit' }
           .spinner.spinner-light
           %span
             Save changes
          
-        = link_to 'Cancel', edit_project_service_path(@project, @service), class: 'btn btn-cancel'
+        = link_to 'Cancel', edit_project_service_path(@project, @service), class: 'btn gl-button btn-cancel'