problem with local builds

[ThomasBreuer]

The CI tests take care of copying certain files in pkg/JuliaInterface/doc/ to docs/src/assets/html/JuliaInterface/.
These files are needed by Documenter.jl for the creation of cross-references to the JuliaInterface manual after the JuliaInterface manual has been built.

When one builds the GAP.jl documentation locally then there is no such automatism yet. If all cross-referenced files exist in docs/src/assets/html/JuliaInterface/ then everything is fine, it not (for example because new cross-references have been added) then Documenter.jl complains (and then it is not obvious from the error messages how one should fix this problem).

Logically, docs/make.jl would be the right place for a command that copies the files.
Should the JuliaInterface manual get processed before that, or would that be too involved?

[fingolfin]

We can add the copying code to docs/make.jl but then we should indeed also run makedoc.g in JuliaInterface. And then the whole "Build GAP manual" step in .github/workflows/CI.yml could go.

It shouldn't be too hard to do that. If anyone is interested in doing it, please go ahead.