Type hash may not be stable

[barche]

See https://github.com/JuliaInterop/CxxWrap.jl/actions/runs/11864776531/job/33068826778?pr=457#step:6:98

We use Base.hash to store the function signature hash, and this failure may indicate that it does what it promises and may not give the same value between Julia runs. Very rarely in this case.