ci: add dev branch to CI pull_request trigger

PR #306 was retargeted from main → dev. The CI workflow
only triggered on pull_request targeting main, so CI silently
stopped running after the retarget.

This adds dev to both push and pull_request branch lists so
CI runs on PRs and pushes targeting dev.

Co-Authored-By: Paperclip <noreply@paperclip.ing>

.github/workflows/ci.yml

@@ -2,9 +2,9 @@ name: CI
 
 on:
   push:
-    branches: [main]
+    branches: [main, dev]
   pull_request:
-    branches: [main]
+    branches: [main, dev]
   workflow_dispatch:
     inputs:
       ref: