Better utf8 invalid test

tests/bulk_operation.rs

@@ -65,7 +65,7 @@ fn test_utf8_invalid() {
     let collection     = client.get_collection("rust_driver_test", "bulk_operation_utf8_invalid");
     let bulk_operation = collection.create_bulk_operation(None);
 
-    let value = unsafe { String::from_utf8_unchecked(b"\xF0\xA4\xAD\xA2".to_vec()) };
+    let value = unsafe { String::from_utf8_unchecked(vec![10, 11, 12, 13, 14, 15, 16, 17]) };
     let document = doc! {"key_1" => value};
     bulk_operation.insert(&document).unwrap();
     assert!(bulk_operation.execute().is_ok());