gh-127521: Mark list as "shared" before resizing if necessary (#127524)

gh-127521: Mark list as "shared" before resizing if necessary (#127524)

In the free threading build, if a non-owning thread resizes a list,
it must use QSBR to free the old list array because there may be a
concurrent access (without a lock) from the owning thread.

To match the pattern in dictobject.c, we just mark the list as "shared"
before resizing if it's from a non-owning thread and not already marked
as shared.