Make DecodeError a subclass of ValueError too

Author: UnknownPlatypus

src/msgspec/_core.c

@@ -22378,7 +22378,7 @@ PyInit__core(void)
     st->DecodeError = PyErr_NewExceptionWithDoc(
         "msgspec.DecodeError",
         "An error occurred while decoding an object",
-        st->MsgspecError, NULL
+        PyTuple_Pack(2, st->MsgspecError, PyExc_ValueError), NULL
     );
     if (st->DecodeError == NULL)
         return NULL;