gh-118331: Don't raise an error if tuple allocation fails when clearing weakrefs (#118338)

It's not safe to raise an exception in `PyObject_ClearWeakRefs()` if one
is not already set, since it may be called by `_Py_Dealloc()`, which
requires that the active exception does not change.

Additionally, make sure we clear the weakrefs even when tuple allocation
fails.