Free-threaded dictionary lookups aren't marking objects as weakref'd

[DinoV]

Bug report

Bug description:

Dictionaries have a fast path which doesn't lock on lookups and a slow path which does. The intention is that the fast-path will succeed after the first slow-path lookup has been passed. But currently we're not parking objects as shared so it always fails.

CPython versions tested on:

CPython main branch

Operating systems tested on:

Linux

Linked PRs

• gh-124642: Dictionaries aren't marking objects as weakref'd #124643
• [3.13] gh-124642: Dictionaries aren't marking objects as weakref'd (GH-124643) #124798