infra: add the missing setup-uv step (#2824)

Author: kevinjqliu

.github/workflows/python-ci.yml

@@ -78,6 +78,8 @@ jobs:
     - uses: actions/setup-python@v6
       with:
         python-version: ${{ matrix.python }}
+    - name: Install UV
+      uses: astral-sh/setup-uv@v7
     - name: Install system dependencies
       run: sudo apt-get update && sudo apt-get install -y libkrb5-dev # for kerberos
     - name: Install