[3.15] gh-156909: Fix AST.__repr__ call getting the _fields attribute (GH-157490) (GH-157596)

(cherry picked from commit 1bfcc3c)

Author: johnslavik

Parser/asdl_c.py

@@ -1480,8 +1480,8 @@ def visitModule(self, mod):
         return PyUnicode_FromFormat("%s(...)", Py_TYPE(self)->tp_name);
     }
 
-    PyObject *fields;
-    if (PyObject_GetOptionalAttr((PyObject *)Py_TYPE(self), state->_fields, &fields) < 0) {
+    PyObject *fields = PyObject_GetAttr((PyObject *)Py_TYPE(self), state->_fields);
+    if (!fields) {
         Py_ReprLeave((PyObject *)self);
         return NULL;
     }