[CI] Upload Doxygen to correct destination

.github/workflows/main.yml

@@ -192,7 +192,7 @@ jobs:
       run: |
         cd build/
         tar cvjf ${{ steps.extract_branch.outputs.branch }}.tar.bz2 doc_doxygen/
-        python -m awscli s3 cp ./${{ steps.extract_branch.outputs.branch }}.tar.bz2 s3://xgboost-docs/ --acl public-read
+        python -m awscli s3 cp ./${{ steps.extract_branch.outputs.branch }}.tar.bz2 s3://xgboost-docs/doxygen/ --acl public-read
       if: github.ref == 'refs/heads/master' || contains(github.ref, 'refs/heads/release_')
       env:
         AWS_ACCESS_KEY_ID: ${{ secrets.AWS_ACCESS_KEY_ID_IAM_S3_UPLOADER }}