Fix not throwing the same error as CPython in test_pathlib.test_expanduser (RustPython#5578)

* Fix not throwing the same error as CPython when trying to expanduser of a non-existent user

Signed-off-by: Hanif Ariffin <[email protected]>

* add pwd test

* Skip pwd test on windows

---------

Signed-off-by: Hanif Ariffin <[email protected]>
Co-authored-by: Jeong YunWon <[email protected]>
Co-authored-by: Jeong, YunWon <[email protected]>

Author: hbina

extra_tests/snippets/stdlib_pwd.py

@@ -0,0 +1,12 @@
+import sys
+# windows doesn't support pwd
+if sys.platform.startswith("win"):
+    exit(0)
+
+from testutils import assert_raises
+import pwd
+
+with assert_raises(KeyError):
+    fake_name = 'fake_user'
+    while pwd.getpwnam(fake_name):
+        fake_name += '1'

vm/src/stdlib/pwd.rs

@@ -59,7 +59,7 @@ mod pwd {
         if pw_name.contains('\0') {
             return Err(exceptions::cstring_error(vm));
         }
-        let user = User::from_name(name.as_str()).map_err(|err| err.into_pyexception(vm))?;
+        let user = User::from_name(name.as_str()).ok().flatten();
         let user = user.ok_or_else(|| {
             vm.new_key_error(
                 vm.ctx