add os.getcwdb function

Lib/test/test_os.py

@@ -141,8 +141,6 @@ class MiscTests(unittest.TestCase):
                 if support.verbose:
                     print(f"Tested current directory length: {len(cwd)}")
 
-    # TODO: RUSTPYTHON (AttributeError: module 'os' has no attribute 'getcwdb')
-    @unittest.expectedFailure
     def test_getcwdb(self):
         cwd = os.getcwdb()
         self.assertIsInstance(cwd, bytes)

vm/src/stdlib/os.rs

@@ -682,6 +682,11 @@ mod _os {
             .to_owned())
     }
 
+    #[pyfunction]
+    fn getcwdb(vm: &VirtualMachine) -> PyResult<Vec<u8>> {
+        Ok(getcwd(vm)?.into_bytes().to_vec())
+    }
+
     #[pyfunction]
     fn chdir(path: PyPathLike, vm: &VirtualMachine) -> PyResult<()> {
         env::set_current_dir(&path.path).map_err(|err| err.into_pyexception(vm))