ci: simplify triggers to avoid duplicate runs

- push to dev: runs tests + version bump
- pull_request to main: runs tests only (gate for merge)
- Added concurrency group to cancel duplicate runs

Author: atomantic

.github/workflows/ci.yml

@@ -1,10 +1,15 @@
 name: CI
 
 on:
-  pull_request:
-    branches: [main, dev]
   push:
-    branches: [dev, main]
+    branches: [dev]
+  pull_request:
+    branches: [main]
+
+# Cancel duplicate runs for the same branch/PR
+concurrency:
+  group: ci-${{ github.head_ref || github.ref }}
+  cancel-in-progress: true
 
 permissions:
   contents: write