gh-158592: Reallocate the list's array when deleting by index (gh-158602)

Author: x42005e1f

Misc/NEWS.d/next/Core_and_Builtins/2026-10-02-16-19-35.gh-issue-158592.V6W21J.rst

@@ -0,0 +1 @@
+``del list[index]`` now triggers shrinking the list's internal array.

Objects/listobject.c

@@ -1182,7 +1182,7 @@ list_ass_item_lock_held(PyListObject *a, Py_ssize_t i, PyObject *v)
         if (i < size - 1) {
             list_shift_items_left_lock_held(a, i, size - 1);
         }
-        Py_SET_SIZE(a, size - 1);
+        list_resize(a, size - 1);  // NB: shrinking a list can't fail
     }
     else {
         FT_ATOMIC_STORE_PTR_RELEASE(a->ob_item[i], Py_NewRef(v));