ci: use uv to build sdist

Why not.

Author: indygreg

.github/workflows/sdist.yml

@@ -17,10 +17,14 @@ jobs:
         with:
           persist-credentials: false
 
+      - name: Install uv
+        uses: astral-sh/setup-uv@d9e0f98d3fc6adb07d1e3d37f3043649ddad06a1 # v6.5.0
+        with:
+          version: "0.8.11"
+
       - name: Build sdist
         run: |
-          python -m pip install -r ci/requirements.txt
-          python setup.py sdist
+          uv build --sdist
 
       - name: Upload sdist
         uses: actions/upload-artifact@ea165f8d65b6e75b540449e92b4886f43607fa02 # v4.6.2