fix: trigger CI on PRs targeting dev branch

The CI workflow was only triggering for PRs to main, but kube-vip#44
is a PR targeting the dev branch. Adding 'dev' to the pull_request
branches list ensures CI runs for all plugin PRs regardless of target.

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

.github/workflows/ci.yaml

@@ -4,7 +4,7 @@ on:
   push:
     branches: [main]
   pull_request:
-    branches: [main]
+    branches: [main, dev]
   workflow_call:
   workflow_dispatch: