gh-111178: Fix function signatures in bytesobject.c

[vstinner]

• Issue: UBSan: Calling a function through pointer to incorrect function type is undefined behavior #111178

[vstinner]

I didn't fix the warning on the signature generated by Argument Clinic:

Objects/descrobject.c:420:24: runtime error: call to function bytes_decode through pointer to incorrect function type 'struct _object *(*)(struct _object *, struct _object *const *, long, struct _object *)'
/home/vstinner/python/main/Objects/clinic/bytesobject.c.h:1034: note: bytes_decode defined here

[vstinner]

cc @picnixz