Warning message when creating a grouped boxplot

When I run the example code for a grouped box plot on the plotly documentation I get a the following warning:

Warning: 'layout' objects don't have these attributes: 'boxmode'
Valid attributes include:
'_deprecated', 'activeshape', 'annotations', 'autosize', 'autotypenumbers', 'calendar', 'clickmode', 'coloraxis', 'colorscale', 'colorway', 'computed', 'datarevision', 'dragmode', 'editrevision', 'editType', 'font', 'geo', 'grid', 'height', 'hidesources', 'hoverdistance', 'hoverlabel', 'hovermode', 'images', 'legend', 'mapbox', 'margin', 'meta', 'metasrc', 'modebar', 'newshape', 'paper_bgcolor', 'plot_bgcolor', 'polar', 'scene', 'selectdirection', 'selectionrevision', 'separators', 'shapes', 'showlegend', 'sliders', 'smith', 'spikedistance', 'template', 'ternary', 'title', 'transition', 'uirevision', 'uniformtext', 'updatemenus', 'width', 'xaxis', 'yaxis', 'barmode', 'bargap', 'mapType'

The code is on the documentation website but reproduced here as a reprex:

fig <- plot_ly(ggplot2::diamonds, x = ~cut, y = ~price, color = ~clarity, type = "box")
fig <- fig %>% layout(boxmode = "group")

fig

I can see that this issue was discussed some years ago but despite the issue being closed it still seems to be a problem.

Reproduce the grouped boxplot example from the Plotly R documentation using the provided reprex and confirm the warning. Read the discussion in issue #994 for relevant context, then trace the R-to-plotly layout handling. Done means the example renders grouped boxes without the invalid boxmode warning.