Fix double decref after failed PyList_SetItem in C tokenizer (#361)

PyList_SetItem steals the item reference even on failure, so the error path must not call Py_DECREF on the same object.

Co-authored-by: Cursor <cursoragent@cursor.com>

src/mwparserfromhell/parser/ctokenizer/tok_parse.c

@@ -1753,7 +1753,6 @@ Tokenizer_handle_single_tag_end(Tokenizer *self)
         return NULL;
     }
     if (PyList_SetItem(self->topstack->stack, index, token)) {
-        Py_DECREF(token);
         return NULL;
     }
     return Tokenizer_pop(self);