`memhash` is to be deleted in 1.13

[adienes]

InMemoryDatasets.jl/src/characters/characters.jl

Line 137 in b02dc59

function Base.hash(s::Characters{N}, h::UInt) where N

it's used here; ref JuliaLang/julia#59151

note that there are some in-progress plans to simplify the migration path but I just wanted to give advance warning