fix build without Py_DEBUG and DNDEBUG (closes #14509)

Objects/stringobject.c

@@ -1262,7 +1262,9 @@ string_hash(PyStringObject *a)
     register unsigned char *p;
     register long x;
 
+#ifdef Py_DEBUG
     assert(_Py_HashSecret_Initialized);
+#endif
     if (a->ob_shash != -1)
         return a->ob_shash;
     len = Py_SIZE(a);

Objects/unicodeobject.c

@@ -6538,7 +6538,9 @@ unicode_hash(PyUnicodeObject *self)
     register Py_UNICODE *p;
     register long x;
 
+#ifdef Py_DEBUG
     assert(_Py_HashSecret_Initialized);
+#endif
     if (self->hash != -1)
         return self->hash;
     len = PyUnicode_GET_SIZE(self);