Fix CI to avoid duplicate runs

Run on push only for main branch, and on pull_request for all branches.
Previously triggered both on every push and every PR, causing duplicate
workflow runs when pushing to a PR branch.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: amis92

.github/workflows/ci.yml

@@ -1,5 +1,8 @@
 name: CI
-on: [push, pull_request]
+on:
+  push:
+    branches: [main]
+  pull_request:
 jobs:
   build:
     strategy: