Add test cases for issue 4381

This was one of the original issues filed against rustfmt that discussed
using a natural sort order instead of a lexicographical order. At the
time it was closed, but now that we're supporting version-sorting in
`style_edition=2024` I thought it would be good to add a test case.

tests/source/issue-4381/style_edition_2015.rs

@@ -0,0 +1,3 @@
+// rustfmt-style_edition: 2015
+
+use std::num::{NonZeroU8, NonZeroU16, NonZeroU32, NonZeroU64};

tests/target/issue-4381/style_edition_2015.rs

@@ -0,0 +1,3 @@
+// rustfmt-style_edition: 2015
+
+use std::num::{NonZeroU16, NonZeroU32, NonZeroU64, NonZeroU8};

tests/target/issue-4381/style_edition_2024.rs

@@ -0,0 +1,3 @@
+// rustfmt-style_edition: 2024
+
+use std::num::{NonZeroU8, NonZeroU16, NonZeroU32, NonZeroU64};