If you explicitly add 'materialized' to the CTE declaration -- that is:

  with dummy_table_name as materialized
    (select stuff from table ...)

the intent becomes explicit. (FWIW, while the nonstandard "materialized" keyword here doesn't have the grammatical form of hints in other DBs, I've still described it in my org as "the only hint Postgres supports" because the closest equivalent in, say, Oracle, is a hint -- the apparently undocumented /+ materialize /)