fixed action

.github/workflows/build.yml

 name: Build Project
 
-on: [push, pull_request]
+on:
+  pull_request:
+  push:
+    branches:
+    - master
 
 jobs:
   build:

.github/workflows/checkstyle.yml

 name: Code Formatter
 
-on: [push]
-
+on:
+  pull_request:
+  push:
+    branches:
+    - master
 jobs:
   format:
     runs-on: ubuntu-latest