Fix: _build dir does not exist in GH Action

Author: hongquan

.github/workflows/build.yml

@@ -60,5 +60,5 @@ jobs:
       - name: Build (Python ${{ matrix.python }})
         run: |
           set -x
-          uv build
+          uv build -C build-dir=_build
           cd _build && uv run --group docs --no-editable -m sphinx -b html -W -v ../docs html