[3.12] gh-58956: Fix a frame refleak in bdb (GH-128190)

[gaogaotiantian]

(cherry picked from commit 767c89b)

Co-authored-by: Tian Gao [email protected]

• Issue: Pdb does not stop at a breakpoint #58956

[gaogaotiantian]

Hey @iritkatriel , had to ping you again because this is related to #125549. It's a bit convoluted but basically this is fixing something that does not exist. This fix is safe, passes the test but it does not really do anything, because enterframe is never assigned. However, with this "fix", we can safely merge #125549 without leaking any frames. The order could be either way but hopefully by merging them closely with each other we don't need to worry about that.