Merge pull request #2690 from cta-observatory/changelog_check_main

Perform changelog check only for pull requsts targeting main

.github/workflows/changelog.yml

@@ -4,6 +4,8 @@ on:
   pull_request:
     # should also be re-run when changing labels
     types: [opened, reopened, labeled, unlabeled, synchronize]
+    branches:
+      - 'main'
 
 env:
   FRAGMENT_NAME_PREFIX: "docs/changes/${{ github.event.number }}"