dirstate: use tuple interface to fix leak in pack_dirstate() Spotted by ASAN. Unlike PyTuple_GET_ITEM(), PySequence_ITEM() returns a new reference. This bug could be fixed by inserting Py_CLEAR() and Py_XDECREF() appropriately, but I think requiring a tuple object is simpler and less error-prone. The cext version is jumped to 10 since 6..9 are used in the default branch. We'll need to bump it again at merge.