A while back we moved the pending calls to PyInterpreterState. Then in 2020 we made it so pending calls would only run in the main thread of the main interpreter. Doing so renders the per-interpreter pending calls state pointless and prevents us from making use of pending calls for subinterpreters.

Linked PRs

• gh-104812: Run Pending Calls in any Thread #104813
• [3.12] gh-104812: Run Pending Calls in any Thread (gh-104813) #105752
• gh-104812: Skip Pending Calls Tests if No Threading #105761