Struct field docstrings do not work for `const` fields of mutable structs

[lhupe]

const fields of mutable structs cannot be annotated with docstrings in the same way as mutable fields, e.g.

"a struct docstring"
mutable struct SomeStruct
    "a field docstring"
    mutablefield
    "another field docstring"
    const constfield
end

results in the following behaviour (tested on v1.11.5 and 1.12.0-beta4)

help?> SomeStruct.mutablefield
  a field docstring

help?> SomeStruct.constfield
  SomeStruct has fields mutablefield, and constfield.

This issue has already been filed with DocStringExtensions (JuliaDocs/DocStringExtensions.jl#155) back in September '24, but it's definitely a Julia problem and I can't find any previous issues here.