[CI] fix possible user permission issues in nightly index generation (#39390)

Signed-off-by: Shengqi Chen <harry-chen@outlook.com>

.buildkite/scripts/generate-and-upload-nightly-index.sh

@@ -19,7 +19,7 @@ has_new_python=$($PYTHON -c "print(1 if __import__('sys').version_info >= (3,12)
 if [[ "$has_new_python" -eq 0 ]]; then
     # use new python from docker
     docker pull python:3-slim
-    PYTHON="docker run --rm -v $(pwd):/app -w /app python:3-slim python3"
+    PYTHON="docker run --rm -u $(id -u):$(id -g) -v $(pwd):/app -w /app python:3-slim python3"
 fi
 
 echo "Using python interpreter: $PYTHON"