fix(ci): restrict push trigger to main branch only

Prevents double CI execution on PR branches (push + pull_request both
triggered, causing duplicate workflow runs).

Signed-off-by: Sebastian Mendel <info@sebastianmendel.de>

Author: CybotTM

.github/workflows/ci.yml

@@ -2,6 +2,7 @@ name: CI
 
 on:
   push:
+    branches: [main]
   pull_request:
   merge_group:
   schedule: