Update tutorial creating a JSO-compliant solver

Need to update https://jso.dev/JSOTutorials.jl/creating-a-jso-compliant-solver/

The function `hess` now returns a `Symmetric` object so no need to add `Symmetric(hess(nlp, x), :L)`.

Open the tutorial at https://jso.dev/JSOTutorials.jl/creating-a-jso-compliant-solver/ and locate the solver code that wraps hess(nlp, x) with Symmetric(..., :L). Update the tutorial to reflect that hess now returns a Symmetric object, then check the rendered tutorial to confirm the outdated wrapper is gone.

Vom Indexierungsmodell aus dem Issue-Text verfasst.