Fix memory leak in path_converter()

Issue #28200: Replace PyUnicode_AsWideCharString() with
PyUnicode_AsUnicodeAndSize().
diff --git a/Modules/posixmodule.c b/Modules/posixmodule.c
index ba54249..470ee92 100644
--- a/Modules/posixmodule.c
+++ b/Modules/posixmodule.c
@@ -920,7 +920,7 @@
 
     if (is_unicode) {
 #ifdef MS_WINDOWS
-        wide = PyUnicode_AsWideCharString(o, &length);
+        wide = PyUnicode_AsUnicodeAndSize(o, &length);
         if (!wide) {
             goto exit;
         }