Fix signature of initObjToJSON (pandas-dev#47466)

Author: hoodmane

pandas/_libs/src/ujson/python/ujson.c

@@ -43,7 +43,7 @@ Numeric decoder derived from TCL library
 
 /* objToJSON */
 PyObject *objToJSON(PyObject *self, PyObject *args, PyObject *kwargs);
-void initObjToJSON(void);
+void *initObjToJSON(void);
 
 /* JSONToObj */
 PyObject *JSONToObj(PyObject *self, PyObject *args, PyObject *kwargs);