fig.cap doesn't work for plotly for html notebook (but work for pure html)

Here is an example Rmd:

---
title: "R Notebook"
output:
  html_notebook:
    fig_caption: yes
  html_document:
    df_print: paged
---

```{r, fig.cap="About cars"}
plot(cars)

library(plotly)
plot_ly(data=cars, x=~speed,y=~dist, type="scatter", mode="markers")



I notice that there is a fix for `knitr` at https://github.com/yihui/knitr/issues/1223 when `fig.cap` also doesn't work for plotly. But The fix seems not applicable to `html_notebook`?

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rstudio / rmarkdown

fig.cap doesn't work for plotly for html notebook (but work for pure html) #1764