DataInspector: fix an attribute extraction bug for heatmaps & images

If the colorrange attribute is left at default it returns
MakieCore.Automatic; the method for `get` that was called at
show_imagelike does not check for this type so the ensuing call to
interpolated_getindex would fail.

This is fixed by calling `get_attribute` instead which calls to_value
and checks if it's an Automatic type which if it is then falls back to
the provided default.

Fixes #3101

src/interaction/inspector.jl

@@ -662,7 +662,7 @@ function show_imagelike(inspector, plot, name, edge_based)
     a._color[] = if z isa AbstractFloat
         interpolated_getindex(
             to_colormap(plot.colormap[]), z,
-            to_value(get(plot.attributes, :colorrange, (0, 1)))
+            get_attribute(plot.attributes, :colorrange, (0, 1))
         )
     else
         z