type_decoder.c: Workaround for a compiler warning.

type_decoder.c: Workaround for a compiler warning.

  type_decoder.c:1040:16: warning: cast between incompatible function types from ‘PyObject * (*)(PyObject *, PyObject *, PyObject *)’ {aka ‘struct _object * (*)(struct _object *, struct _object *, struct _object *)’} to ‘PyObject * (*)(PyObject *, PyObject *)’ {aka ‘struct _object * (*)(struct _object *, struct _object *)’} [-Wcast-function-type]
   1040 |  { "register", (PyCFunction)Decoder_register, METH_VARARGS|METH_KEYWORDS,
        |                ^