ci: prevent always removing ok-to-test label

The check for a rebase always hits, but the actions for that inspect the
event for a real rebase. Removing the `ok-to-test` label is not suitable
in the Mergify check, as the label action does not inspect the event.
This caused the `ok-to-test` label to be removed on every Mergify
validation of the PR.

Fixes: ba68ce6 (ci: drop `ok-to-test` label when a PR is rebased)
Signed-off-by: Niels de Vos <ndevos@redhat.com>

.mergify.yml

@@ -63,9 +63,6 @@ pull_request_rules:
       dismiss_reviews:
         approved: true
         changes_requested: false
-      label:
-        remove:
-          - ok-to-test
 
   - name: ask to resolve conflict
     conditions: