`StenoGraphs` has to be loaded manually

[Maximilian-Stefan-Ernst]

There seems to be a bug where the StenoGraphs package has to be loaded additionally.

Installing SEM.jl in a fresh environment, and trying to run a model, leads to the error

ERROR: UndefVarError: `StenoGraphs.SimpleNode` not defined in `Main`
Suggestion: check for spelling errors or missing imports.
Stacktrace:
 [1] top-level scope
   @ REPL[7]:1

Code to reproduce:

using StructuralEquationModels

observed_vars = [:x1, :x2, :x3, :y1, :y2, :y3, :y4, :y5, :y6, :y7, :y8]
latent_vars = [:ind60, :dem60, :dem65]

graph = @StenoGraph begin

    # loadings
    ind60 → fixed(1) * x1 + x2 + x3
    dem60 → fixed(1) * y1 + y2 + y3 + y4
    dem65 → fixed(1) * y5 + y6 + y7 + y8

    # latent regressions
    label(:a) * dem60 ← ind60
    label(:b) * dem65 ← dem60
    label(:c) * dem65 ← ind60

    # variances
    _(observed_vars) ↔ _(observed_vars)
    _(latent_vars) ↔ _(latent_vars)

    # covariances
    y1 ↔ y5
    y2 ↔ y4 + y6
    y3 ↔ y7
    y8 ↔ y4 + y6

    Symbol(1) → _(observed_vars)
end