fix: replace Python::with_gil with Python::attach for pyo3 0.28

pyo3 0.28 renamed Python::with_gil to Python::attach.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: JanKaul

datafusion_iceberg/tests/integration_pyiceberg.rs

@@ -207,7 +207,7 @@ async fn test_pyiceberg_integration() {
     assert!(found_63700, "Product 63700 not found in results");
 
     // Now use PyIceberg to read the same table
-    Python::with_gil(|py| {
+    Python::attach(|py| {
         // Configure venv if available
         configure_python_venv(py).expect("Failed to configure Python venv");