pythongh-94673: Ensure subtypes are readied only once in math.trunc() (pythongh-105465)

Fixes a typo in d2e2e53.
(cherry picked from commit 5394bf9)

Co-authored-by: neonene <[email protected]>

Author: neonene

Modules/mathmodule.c

@@ -2067,7 +2067,7 @@ math_trunc(PyObject *module, PyObject *x)
         return PyFloat_Type.tp_as_number->nb_int(x);
     }
 
-    if (_PyType_IsReady(Py_TYPE(x))) {
+    if (!_PyType_IsReady(Py_TYPE(x))) {
         if (PyType_Ready(Py_TYPE(x)) < 0)
             return NULL;
     }