fix clippy tests

tests/by-util/test_df.rs

@@ -3,6 +3,13 @@
 // For the full copyright and license information, please view the LICENSE
 // file that was distributed with this source code.
 // spell-checker:ignore udev pcent iuse itotal iused ipcent
+#![allow(
+    clippy::similar_names,
+    clippy::cast_possible_truncation,
+    clippy::cast_sign_loss,
+    clippy::float_cmp
+)]
+
 use std::collections::HashSet;
 
 use crate::common::util::TestScenario;