Error message text color is too subtle with Bootstrap 5

[cpsievert]

In #3914, the text color of error messages changed from red to --bs-danger-text-emphasis, which I think was designed to be put on a danger bg, and IMO is too close to black for error messages. Perhaps --bs-danger would be better @gadenbuie?

library(shiny)
library(bslib)

ui <- page_fixed(
  textOutput("foo")
)

server <- function(input, output, session) {
  output$foo <- renderText({1+"a"})
}

shinyApp(ui, server)