Not properly checking for invalid escape seqeunce \X

[hbina]

Summary

RustPython doesn't report any errors running the file RustPython/extra_tests/snippets/builtin_bytes.py

cargo run --release -- /home/hbina085/git/RustPython/extra_tests/snippets/builtin_bytes.py 
    Finished `release` profile [optimized] target(s) in 0.15s
     Running `target/release/rustpython /home/hbina085/git/RustPython/extra_tests/snippets/builtin_bytes.py`

Expected

But CPython does,

python /home/hbina085/git/RustPython/extra_tests/snippets/builtin_bytes.py 
/home/hbina085/git/RustPython/extra_tests/snippets/builtin_bytes.py:23: SyntaxWarning: invalid escape sequence '\X'
  assert b"omkmok\Xaa" == bytes([111, 109, 107, 109, 111, 107, 92, 88, 97, 97])

The issue is that RustPython does not check if \X is a valid escape sequence.

[youknowone]

Could you share cpython version? We run every test under extra_tests/snippets/ using CPython to ensure the result are the same on both side. Maybe the warning isn't checked in the CI..?