`cp -a` still fails with readonly directories (follow-up to #7961)

[sylvestre]

PR #10529 fixed cp -r but cp -a still fails with "Permission denied" on readonly directories.

Reproduction

sudo rm -rf test_a test_gnu
mkdir -p test_a/b && touch test_a/b/file.txt && chmod -R -w test_a

# GNU cp -a (works)
/usr/bin/cp -a test_a test_gnu
echo $?
# 0
stat --format=%a test_gnu
# 555

sudo  rm -rf test_a test_gnu

mkdir -p test_a/b && touch test_a/b/file.txt && chmod -R -w test_a
# uutils cp -a (fails)
cargo run --features unix -q -- cp -a test_a test_uutils_a
# cp: Permission denied (os error 13)
echo $?
# 1

output:

0
555
cp: Permission denied (os error 13)
1

[sylvestre]

@nikolalukovic if you want to have a look :)

[nikolalukovic]

On it 🙂

[sylvestre]

follow up of:
#7961