chore(ci): fix changelog action for non-main base branches

.github/workflows/changelog-checker.yml

@@ -36,7 +36,7 @@ jobs:
             changelog_file_path=".changelog/[_0-9]*.txt"
           fi
 
-          changelog_files=$(git --no-pager diff --name-only HEAD "$(git merge-base HEAD "origin/main")" | egrep ${changelog_file_path})
+          changelog_files=$(git --no-pager diff --name-only HEAD "$(git merge-base HEAD "origin/${{ github.event.pull_request.base.ref }}")" | egrep -e "${changelog_file_path}"))
 
           # If we do not find a file in .changelog/, we fail the check
           if [ -z "$changelog_files" ]; then