gh-120838: Make Sure Py_Finalize() Always Runs Against the Main Interpreter

[ericsnowcurrently]

We can't easily force Py_Finalize() to run in the main thread (especially because of Py_Exit()), but we can at least ensure the main interpreter is active.

(We'll be backporting this since the fix for gh-120765 needs it.)

• Issue: Some Runtime Finalization Constraints Are Not Enforced Nor Documented #120838

[ericsnowcurrently]

FYI, this causes gh-120765 to be triggered more often, so we'll need to fold it into the fix for that issue: gh-121060.