ci: fix run on pull requests (#56)

Author: Kikobeats

.github/workflows/pull_request.yml

@@ -1,16 +1,10 @@
 name: pull_request
 
 on:
-  push:
-    branches:
-      - master
   pull_request:
-    branches:
-      - master
 
 jobs:
   test:
-    if: github.ref != 'refs/heads/master'
     runs-on: ubuntu-latest
     steps:
       - name: Checkout