gh-125843: fix test_curses.test_attributes on x86-64 macOS (#134252)

While some `libcurses` functions are meant to return OK on success,
this is not always the case for all implementations. As such, we relax
the checks on the return values and allow any non-ERR value to be
considered equivalent to OK.

Author: picnixz

Modules/_cursesmodule.c

@@ -392,17 +392,16 @@ _PyCursesStatefulCheckFunction(PyObject *module,
  */
 
 /*
- * Return None if 'code' is OK. Otherwise, set an exception
- * using curses_set_error() and the remaining arguments, and
- * return NULL.
+ * Return None if 'code' is different from ERR (implementation-defined).
+ * Otherwise, set an exception using curses_set_error() and the remaining
+ * arguments, and return NULL.
  */
 static PyObject *
 curses_check_err(PyObject *module, int code,
                  const char *curses_funcname,
                  const char *python_funcname)
 {
     if (code != ERR) {
-        assert(code == OK);
         Py_RETURN_NONE;
     }
     curses_set_error(module, curses_funcname, python_funcname);
@@ -416,7 +415,6 @@ curses_window_check_err(PyCursesWindowObject *win, int code,
                         const char *python_funcname)
 {
     if (code != ERR) {
-        assert(code == OK);
         Py_RETURN_NONE;
     }
     curses_window_set_error(win, curses_funcname, python_funcname);
@@ -1580,7 +1578,7 @@ _curses_window_derwin_impl(PyCursesWindowObject *self, int group_left_1,
     win = derwin(self->win,nlines,ncols,begin_y,begin_x);
 
     if (win == NULL) {
-        curses_window_set_error(self, "derwin", NULL);
+        curses_window_set_null_error(self, "derwin", NULL);
         return NULL;
     }