Replace documentation example of "Blacklist" join query

[albe]

https://github.com/doctrine/orm/blob/master/docs/en/reference/dql-doctrine-query-language.rst#arbitrary-join

shows an example of a join query with a "Blacklist" table. This could easily be changed to a more sensible example. I would suggest "Banlist" as alternative example.

[lsmith77]

FYI Symfony has a similar PR where the term "blocklist" is suggested symfony/symfony-docs#13769