Use .has-tooltip as suggested at:

https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/4093#note_12533926

app/views/projects/runners/_runner.html.haml

@@ -5,8 +5,7 @@
       - if @runners.include?(runner)
         = link_to runner.short_sha, runner_path(runner)
         - if runner.locked?
-          %small{title: 'Exclusive to this project'}
-            = icon('lock')
+          = icon('lock', class: 'has-tooltip', title: 'Exclusive to this project')
         %small
           = link_to edit_namespace_project_runner_path(@project.namespace, @project, runner) do
             %i.fa.fa-edit.btn