gh-161021: Fix the error code reported by winreg.ExpandEnvironmentStrings()

Author: aisk

Misc/NEWS.d/next/Windows/2026-11-01-02-46-37.gh-issue-161021.cogwdI.rst

@@ -0,0 +1,2 @@
+Fix the error code reported by :func:`winreg.ExpandEnvironmentStrings` when
+expanding the string fails.

PC/winreg.c

@@ -1262,7 +1262,7 @@ winreg_ExpandEnvironmentStrings_impl(PyObject *module, const wchar_t *string)
     rc = ExpandEnvironmentStringsW(string, retValue, retValueSize);
     if (rc == 0) {
         PyMem_Free(retValue);
-        return PyErr_SetFromWindowsErrWithFunction(retValueSize,
+        return PyErr_SetFromWindowsErrWithFunction(0,
                                         "ExpandEnvironmentStrings");
     }
     o = PyUnicode_FromWideChar(retValue, -1);