Add PR trigger to CI workflow (#57)

Author: DavidMazarro

.github/workflows/main.yml

@@ -5,7 +5,13 @@
 
 name: CI
 
-on: push
+on: 
+  pull_request: 
+    branches:
+      - main
+  push:
+    branches:
+      - main
 
 concurrency:
   group: build-${{ github.ref }}