missing function in plot recipe

[xzackli]

_lookup_to_axis doesn't appear to be defined anywhere, but is used in the Makie recipe.

https://github.com/rafaqz/DimensionalData.jl/blob/d10d0fc6bd2021487762d93eb711fb8084f7f567/ext/DimensionalDataMakie.jl#L384

[rafaqz]

Ahh right I just changed it, we mustn't test plots going through that dispatch.

Do you have an example I can put in the tests?