ci: run scheduled pipelines biweekly

No need to run with more frequency to just check infra.

Author: msune

.github/workflows/ci.yaml

@@ -4,7 +4,7 @@ on:
   push:
   pull_request:
   schedule:
-    - cron: '0 0 * * *'  # every day at midnight
+    - cron: '0 0 1,15 * *'  # biweekly (1st and 15th of each month)
 
 env:
   ACTIONS_ALLOW_USE_UNSECURE_NODE_VERSION: true