run update.yaml every 12min

The job takes over 5 minutes most of the time anyway, so this might help
us have GitHub actually schedule the job at the asked interval :)

Signed-off-by: Benjamin Cabé <benjamin@zephyrproject.org>

Author: kartben

.github/workflows/update.yaml

@@ -2,7 +2,7 @@ name: Update and publish
 
 on:
   schedule:
-    - cron: '*/5 * * * *'
+    - cron: '*/12 * * * *'
   push:
     branches:
       - main