tests: use platform path separator in symlink content

Appears that this was the reason why we got the error "The filename, directory
name, or volume label syntax is incorrect" on Windows CI.

lib/tests/test_local_working_copy.rs

@@ -17,6 +17,7 @@ use std::os::unix::fs::PermissionsExt;
 #[cfg(unix)]
 use std::os::unix::net::UnixListener;
 use std::path::Path;
+use std::path::PathBuf;
 use std::sync::Arc;
 
 use assert_matches::assert_matches;
@@ -1324,7 +1325,11 @@ fn test_check_out_existing_file_symlink_icase_fs(victim_exists: bool) {
 
     // Creates a symlink in working directory, and a tree that will overwrite
     // the symlink content.
-    try_symlink("../pwned", workspace_root.join("parent")).unwrap();
+    try_symlink(
+        PathBuf::from_iter(["..", "pwned"]),
+        workspace_root.join("parent"),
+    )
+    .unwrap();
     let victim_file_path = workspace_root.parent().unwrap().join("pwned");
     if victim_exists {
         std::fs::write(&victim_file_path, "old").unwrap();