Fix Windows test to copy testdata

tests/windows.rs

@@ -7,17 +7,18 @@
 use predicates::prelude::*;
 
 mod util;
-use util::run;
+use util::{copy_of_testdata, run};
 
 /// Only on Windows, backslash can be used as a path separator in filters.
 #[test]
 fn list_mutants_well_tested_exclude_folder_containing_backslash_on_windows() {
     // This could be written more simply as `--exclude module` but we want to
     // test that backslash is accepted.
+    let tmp = copy_of_testdata("with_child_directories");
     run()
         .arg("mutants")
         .args(["--list", "--exclude", "**\\module\\**\\*.rs"])
-        .current_dir("testdata/with_child_directories")
+        .current_dir(tmp.path())
         .assert()
         .stdout(
             predicates::str::contains(r"src/module")