[3.11] gh-87115: Set `__main__.__spec__` to `None` in pdb (GH-116141) (#116155)

* gh-87115: Set `__main__.__spec__` to `None` in pdb (#116141)

(cherry picked from commit ccfc042bbf31e53c44b8aae444afd8365b798422)

* [3.11] gh-87115: Set `__main__.__spec__` to `None` in pdb (GH-116141)
(cherry picked from commit ccfc042bbf31e53c44b8aae444afd8365b798422)

Co-authored-by: Tian Gao <gaogaotiantian@hotmail.com>