Currently the variable PyStructSequence_UnnamedField has type "char *". It is used as a special value for setting to the name field of PyStructSequence_Field. But the type of the name field is "const char *".

I propose to change the declaration of PyStructSequence_UnnamedField to "const char * const". Makes it referring to immutable character string and make it itself immutable.

It is binary compatible change, but some user code can complain at compilation time if it uses PyStructSequence_UnnamedField in unusual way (assigns to the "char *" variable, etc). It is very unlikely.