mktemp: fix fmt of test_prefix_template_separator

tests/by-util/test_mktemp.rs

@@ -575,9 +575,7 @@ fn test_template_path_separator() {
 /// Test that a prefix with a point is valid.
 #[test]
 fn test_prefix_template_separator() {
-    new_ucmd!()
-        .args(&["-t", TEST_TEMPLATE9])
-        .succeeds();
+    new_ucmd!().args(&["-t", TEST_TEMPLATE9]).succeeds();
 }
 
 /// Test that a suffix with a path separator is invalid.