ci(github actions): add 'master' to the 'pull_request' section

Closes #159

Author: rafamizes

.github/workflows/build.yml

@@ -7,9 +7,12 @@ on:
   # Triggers the workflow on push or pull request events but only for the main branch
   # Runs this action when you push on master
   push:
-    branches: [master]
+    branches:
+      - master
   # Runs this when a PR against master is created
   pull_request:
+    branches:
+      - master
 
   # Allows you to run this workflow manually from the Actions tab
   workflow_dispatch: