Include 'promote' event to include 'cron'

Without the promote event, cron will end up in the actual configuration.
This can be tested by running the 'drone fmt' command on the .drone.yml
file. Also mentioned here: harness/harness#2705

.drone.yml

@@ -9,6 +9,8 @@ steps:
       - echo test
 
 trigger:
+  event:
+    - promote
   cron:
     - update-repository-every-hour
 
@@ -70,7 +72,6 @@ volumes:
 
 trigger:
   event:
-    exclude:
-      - "*"
+    - promote
   cron:
     - learn-new-models-every-day