Problems in calling multiprocess functions on github actions

I am writing a Julia course, where the script is compiled to MD and then to HTML using Literate.jl and Documenter.jl on GitHub actions.

The problem is in this snippet:

using Distributed, BenchmarkTools
a = rand(1:35,100)
@everywhere function fib(n)
    if n == 0 return 0 end
    if n == 1 return 1 end
    return fib(n-1) + fib(n-2)
result  = pmap(fib,a) 

complete script

With GitHub action complaining LoadError: UndefVarError: fib not defined.
Where is the problem? On my PC it works correctly, as I “send” the Fibonacci function to every process with @everywhere

It seems to be more general, GitHub actions raise errors on any call on multiprocess functions, also when I use the @distributed macro :-/