chore: use less concurred minute of hour for scheduled jobs (googleapis#26435)

See https://docs.github.com/en/actions/writing-workflows/choosing-when-your-workflow-runs/events-that-trigger-workflows#schedule

> The schedule event can be delayed during periods of high loads of GitHub Actions workflow runs. High load times include the start of every hour. If the load is sufficiently high enough, some queued jobs may be dropped. To decrease the chance of delay, schedule your workflow to run at a different time of the hour.

Author: diegomarquezp

.github/workflows/codegen.yaml

@@ -1,7 +1,8 @@
 on:
   schedule:
-  # Runs at 12:30, 1:30 and 2:30.
-  - cron: '30 0-2 * * *'
+  # Runs at 12:18, 1:18 and 2:18.
+  # See https://docs.github.com/en/actions/writing-workflows/choosing-when-your-workflow-runs/events-that-trigger-workflows#schedule
+  - cron: '18 0-2 * * *'
   workflow_dispatch:
 
 name: codegen
@@ -18,7 +19,7 @@ jobs:
         with:
           script: |
             console.log('checking size of services')
-            const MAX_SERVICE_SIZE = 300 // 00:30 to 02:30 implies 3 batches of size 100
+            const MAX_SERVICE_SIZE = 300 // 00:18 to 02:18 implies 3 batches of size 100
             const services = ${{ needs.discovery.outputs.services }}
             if (services.length > MAX_SERVICE_SIZE) {
               throw new Error(`Total services (${services.length}) exceed limit of ${MAX_SERVICE_SIZE}`)