[RM-8306] FilterList eq operator surchage does not work as intended

Created on 2023-09-19 14:52:58 by Thomas Bedrine. % Done: 100

The @_eq_@ function that allows a surcharge of the == operator only checks inclusion of an object into the other, and does not actually check if they are equal.

MR https://gitlab.lam.fr/CPF/cpf-redshift/-/merge_requests/544