Update CI.yml

Author: yebai

.github/workflows/CI.yml

@@ -3,12 +3,8 @@ name: CI
 on:
   push:
     branches:
-      # This is where pull requests from "bors r+" are built.
-      - staging
-      # This is where pull requests from "bors try" are built.
-      - trying
-      # Build the main branch.
-      - main
+      - master
+  pull_request:
 
 jobs:
   test: