config is not overwritting `ModeBarButtons` slot

I have noticed that after placing a ModeBarButtons configuration, it is not overwritten / updated downstream.

Reproducible example:

library(plotly)
#> Loading required package: ggplot2
#> 
#> Attaching package: 'plotly'
#> The following object is masked from 'package:ggplot2':
#> 
#>     last_plot
#> The following object is masked from 'package:stats':
#> 
#>     filter
#> The following object is masked from 'package:graphics':
#> 
#>     layout
  # This plotly only has the `toImage` modeBarButton
  plot1 <- plot_ly() %>%
    config(displaylogo = FALSE) %>%
    config(modeBarButtons = list(list("toImage")))
  plot1$x$config$modeBarButtons
#> [[1]]
#> [[1]][[1]]
#> [1] "toImage"
  
  # This plotly also has the `toImage` modeBarButton only
  plot2 <- plot_ly() %>%
    config(displaylogo = FALSE) %>%
    config(modeBarButtons = list(list("toImage"))) %>% 
    config(modeBarButtons = list(list("zoom")))
  plot2$x$config$modeBarButtons
#> [[1]]
#> [[1]][[1]]
#> [1] "toImage"

^{Created on 2022-11-29 with reprex v2.0.2}

This holds true for config(modeBarButtonsToAdd ...)

从 config() 入口开始，重现 issue 中的两个示例，比较 plot1$x$config$modeBarButtons 与 plot2$x$config$modeBarButtons。当后续的 modeBarButtons 配置能够更新之前的值，并且对 modeBarButtonsToAdd 验证出相同的行为时，修复就完成了。