Address new clippy lints

Ran `cargo clippy --all-targets --workspace` and fixed a few minor issues

Author: nyurik

src/uucore/src/lib/features/buf_copy.rs

@@ -49,6 +49,7 @@ mod tests {
             .read(true)
             .write(true)
             .create(true)
+            .truncate(true)
             .open(temp_dir.path().join("file.txt"))
             .unwrap()
     }

src/uucore/src/lib/features/format/spec.rs

@@ -580,29 +580,29 @@ mod tests {
                 Some((42, false)),
                 resolve_asterisk_width(
                     Some(CanAsterisk::Asterisk),
-                    vec![FormatArgument::SignedInt(42)].iter()
+                    [FormatArgument::SignedInt(42)].iter()
                 )
             );
             assert_eq!(
                 Some((42, false)),
                 resolve_asterisk_width(
                     Some(CanAsterisk::Asterisk),
-                    vec![FormatArgument::Unparsed("42".to_string())].iter()
+                    [FormatArgument::Unparsed("42".to_string())].iter()
                 )
             );
 
             assert_eq!(
                 Some((42, true)),
                 resolve_asterisk_width(
                     Some(CanAsterisk::Asterisk),
-                    vec![FormatArgument::SignedInt(-42)].iter()
+                    [FormatArgument::SignedInt(-42)].iter()
                 )
             );
             assert_eq!(
                 Some((42, true)),
                 resolve_asterisk_width(
                     Some(CanAsterisk::Asterisk),
-                    vec![FormatArgument::Unparsed("-42".to_string())].iter()
+                    [FormatArgument::Unparsed("-42".to_string())].iter()
                 )
             );
         }
@@ -631,29 +631,29 @@ mod tests {
                 Some(42),
                 resolve_asterisk_precision(
                     Some(CanAsterisk::Asterisk),
-                    vec![FormatArgument::SignedInt(42)].iter()
+                    [FormatArgument::SignedInt(42)].iter()
                 )
             );
             assert_eq!(
                 Some(42),
                 resolve_asterisk_precision(
                     Some(CanAsterisk::Asterisk),
-                    vec![FormatArgument::Unparsed("42".to_string())].iter()
+                    [FormatArgument::Unparsed("42".to_string())].iter()
                 )
             );
 
             assert_eq!(
                 Some(0),
                 resolve_asterisk_precision(
                     Some(CanAsterisk::Asterisk),
-                    vec![FormatArgument::SignedInt(-42)].iter()
+                    [FormatArgument::SignedInt(-42)].iter()
                 )
             );
             assert_eq!(
                 Some(0),
                 resolve_asterisk_precision(
                     Some(CanAsterisk::Asterisk),
-                    vec![FormatArgument::Unparsed("-42".to_string())].iter()
+                    [FormatArgument::Unparsed("-42".to_string())].iter()
                 )
             );
         }