rustPlatform.importCargoLock: use cp -L again, but ignore error

We accidentally broke the dereferencing logic of copying in https://github.com/NixOS/nixpkgs/pull/379049

The new solution is just to revert back to using `cp -L` but to also ignore the
non-zero exit code with the || operator

pkgs/build-support/rust/import-cargo-lock.nix

@@ -228,7 +228,7 @@ let
         echo Found crate ${pkg.name} at $crateCargoTOML
         tree=$(dirname $crateCargoTOML)
 
-        ${python3Packages.python.interpreter} -c 'import sys, shutil; shutil.copytree(sys.argv[1], sys.argv[2], ignore_dangling_symlinks=True)' "$tree" "$out"
+        cp -prvL "$tree" "$out" || echo "Warning: certain files couldn't be copied!" >&2
         chmod u+w $out
 
         if grep -q workspace "$out/Cargo.toml"; then