fix backport script again

Author: buffalojoec

.github/actions/backport/action.yml

@@ -63,7 +63,7 @@ runs:
         git push origin $BACKPORT_BRANCH
 
         gh pr create \
-          --base $BASE_BRANCH \
+          --base ${{ inputs.base_branch }} \
           --head $BACKPORT_BRANCH \
-          --title "Backport PR #${{ env.PR_NUMBER }} to $BASE_BRANCH" \
-          --body "This is an automated backport of PR #${{ env.PR_NUMBER }} to the $BASE_BRANCH branch."
+          --title "Backport PR #${{ env.PR_NUMBER }} to ${{ inputs.base_branch }}" \
+          --body "This is an automated backport of PR #${{ env.PR_NUMBER }} to the ${{ inputs.base_branch }} branch."