tests: fix "unused import" warnings on Windows

tests/by-util/test_last.rs

@@ -4,8 +4,10 @@
 // file that was distributed with this source code.
 // spell-checker:ignore (words) symdir somefakedir
 
+#[cfg(unix)]
 use crate::common::util::TestScenario;
 
+#[cfg(unix)]
 use regex::Regex;
 use std::fs;
 use std::io::Write;

tests/by-util/test_setsid.rs

@@ -161,7 +161,7 @@ mod unix {
 
 #[cfg(not(target_family = "unix"))]
 mod non_unix {
-    use crate::common::util::{TestScenario, UCommand};
+    use crate::common::util::TestScenario;
 
     #[test]
     fn unsupported_platforms() {