gh-143200: fix UAFs in `Element.__{set,get}item__` when the element is concurrently mutated#143226

picnixz wants to merge 4 commits intopython:mainpython/cpython:mainfrom

picnixz:fix/xml/uaf-in-sub-143200picnixz/cpython:fix/xml/uaf-in-sub-143200Copy head branch name to clipboard