Ensure CLA is sorted before telling bors to merge

Even if the CLA does not require signatures for dependabot
it still needs to mark the PR as OK which may not happen
if the service is done.

Author: Franck Royer

.mergify.yml

@@ -6,6 +6,7 @@ pull_request_rules:
       - "status-success=build (windows)"
       - "status-success=build (ubuntu)"
       - "status-success=e2e_test"
+      - "status-success=license/cla"
       - "author:dependabot-preview[bot]"
     actions:
       comment: