Bug 1649168: Add a cron target that will trigger scriptworker canaries; r=rail

This cron target will be triggered from cloudops' Jenkins.

Differential Revision: https://phabricator.services.mozilla.com/D82822

.cron.yml

@@ -297,3 +297,10 @@ jobs:
           - mozilla-central
       when:
           - {hour: 4, minute: 00}
+
+    - name: scriptworker-canary
+      job:
+          type: trigger-action
+          action-name: scriptworker-canary
+          include-cron-input: true
+      when: []  # never (hook only)