gh-117139: Fix a few _PyStackRef related bugs (#122831)

`BUILD_SET` should use a borrow instead of a steal. The cleanup in `_DO_CALL`
`CONVERSION_FAILED` was incorrect.

Co-authored-by: Ken Jin <[email protected]>

Author: colesbury

Python/bytecodes.c

@@ -1714,11 +1714,10 @@ dummy_func(
             }
             int err = 0;
             for (int i = 0; i < oparg; i++) {
-                PyObject *item = PyStackRef_AsPyObjectSteal(values[i]);
                 if (err == 0) {
-                    err = PySet_Add(set_o, item);
+                    err = PySet_Add(set_o, PyStackRef_AsPyObjectBorrow(values[i]));
                 }
-                Py_DECREF(item);
+                PyStackRef_CLOSE(values[i]);
             }
             if (err != 0) {
                 Py_DECREF(set_o);
@@ -3235,7 +3234,10 @@ dummy_func(
             /* Callable is not a normal Python function */
             STACKREFS_TO_PYOBJECTS(args, total_args, args_o);
             if (CONVERSION_FAILED(args_o)) {
-                DECREF_INPUTS();
+                PyStackRef_CLOSE(callable);
+                for (int i = 0; i < total_args; i++) {
+                    PyStackRef_CLOSE(args[i]);
+                }
                 ERROR_IF(true, error);
             }
             PyObject *res_o = PyObject_Vectorcall(