New since 4.9.3: add_annotations misaligns text when `x` or `y` are factors

Hi,

when running the code below with plotly version 4.9.3,
the annotated text is not aligned to the respective cells.
With plotly version 4.9.2.1 however, it matches nicely.

#devtools::install_version("plotly", version="4.9.2.1")
library(plotly)

Grid <- expand.grid(x=1:3,y=4:6)
Grid <- cbind(Grid, z=rnorm(9))
Grid$xFac <- as.character(Grid$x)
Grid$yFac <- as.factor(Grid$y)

plot_ly(
  data=Grid,
  x=~xFac, y=~yFac, z=~z,
  type='heatmap') %>%
  add_annotations(
    text = letters[1:9], showarrow = FALSE)

Start by running the provided R example with plotly 4.9.3 and compare its annotation alignment with 4.9.2.1, focusing on add_annotations with factor x and y values. Done means the annotated letters align with their heatmap cells in the affected version as they did previously.