Add base parameter to create-pull-request in check-branch-alias workflow

Co-authored-by: swissspidy <841956+swissspidy@users.noreply.github.com>

Author: Copilot

.github/workflows/reusable-check-branch-alias.yml

@@ -129,6 +129,7 @@ jobs:
         uses: peter-evans/create-pull-request@v8
         with:
           token: ${{ secrets.GITHUB_TOKEN }}
+          base: ${{ github.event.repository.default_branch }}
           commit-message: "Update branch-alias to ${{ steps.check_alias.outputs.expected_alias }}"
           title: "Update branch-alias to ${{ steps.check_alias.outputs.expected_alias }}"
           body: |