Prevent CI from triggering twice when creating a PR

Author: SanderMertens

.github/workflows/ci.yml

@@ -1,6 +1,15 @@
 name: CI
 
-on: [ push, pull_request ]
+on:
+  push:
+    branches:
+      - master
+  pull_request:
+    types:
+      - opened
+      - reopened
+      - synchronize
+      - ready_for_review
 
 concurrency:
   group: ${{ github.workflow }}-${{ github.ref }}