adjust workflow triggers

Author: blink1073

.github/workflows/tests.yml

@@ -1,6 +1,12 @@
 name: Tests
 
-on: [push]
+on:
+  push:
+    branches: ["master"]
+  pull_request:
+  # Run once a day.
+  schedule:
+    - cron: "0 8 * * *"
 
 concurrency:
   group: 'tests-${{ github.head_ref || github.run_id }}'