[ci] Optimize AutoTestCI trigger timing.

.github/workflows/action_utest.yml

 name: AutoTestCI
 
 # Controls when the action will run. Triggers the workflow on push or pull request
-on: [push, pull_request]
+# events but only for the master branch
+on:
+  # Runs at 16:00 UTC (BeiJing 00:00) on the 1st of every month
+  schedule:
+    - cron:  '0 16 1 * *'
+  push:
+    branches:
+      - master
+    paths-ignore:
+      - documentation/**
+      - '**/README.md'
+      - '**/README_zh.md'
+  pull_request:
+    branches:
+      - master
+    paths-ignore:
+      - documentation/**
+      - '**/README.md'
+      - '**/README_zh.md'
 
 jobs:
   test: