ci: do a full cron build every day, and limit builds per push or pr (#15839)

.github/workflows/build.yml

@@ -8,6 +8,14 @@ on:
     paths-ignore:
       - 'docs/**'
       - '*.md'
+  schedule:
+    #        ┌────────────── minute (0 - 59)
+    #        │  ┌───────────── hour (0 - 23)
+    #        │  │ ┌───────────── day of the month (1 - 31)
+    #        │  │ │ ┌───────────── month (1 - 12 or JAN-DEC)
+    #        │  │ │ │ ┌───────────── day of the week (0 - 6 or SUN-SAT)
+    #        │  │ │ │ │
+    - cron: '0 18 * * *'
 
 concurrency:
   group: ${{ github.workflow }}-${{ github.event.pull_request.number || github.run_id }}
@@ -17,6 +25,7 @@ jobs:
   controller:
     name: 'Create test plan'
     runs-on: 'ubuntu-latest'
+    if: ${{ (github.event_name == 'schedule' && github.repository == 'libsdl-org/sdl') || github.event_name != 'schedule' }}
     outputs:
       platforms-level1: ${{ steps.plan.outputs.platforms-level1 }}
       platforms-others: ${{ steps.plan.outputs.platforms-others }}
@@ -38,6 +47,7 @@ jobs:
           $EOF
 
           python .github/workflows/create-test-plan.py \
+            ${{ (github.event_name != 'schedule' && '--priority-only') || '' }} \
             --github-variable-prefix platforms \
             --github-ci \
             --verbose \