Build on pull request

.github/workflows/build.yml

@@ -1,11 +1,11 @@
 name: Build and test
-on: [push]
+on: [push, pull_request]
 
 jobs:
   build:
 
     runs-on: ubuntu-latest
-    
+
     steps:
     - uses: actions/checkout@v2
     - name: install packages