gh-37194: Fix typo in pycore_long.h for Python <= 3.8.
This fixes the same issue as in
https://github.com/sagemath/cypari2/pull/146.
Typo was added in dc71bd0.
URL: https://github.com/sagemath/sage/pull/37194
Reported by: Ján Jančár
Reviewer(s): Gonzalo Tornaría, Sebastian Spindler