Bootstrap navbar variables not working in bslib 0.6.1 but working in 0.5

@gadenbuie and @cpsievert asked me to report this bug so I'm not following the guidelines :)

I'm finding that the bootstrap 5 navbar variables are not working for me using bslib version 0.6.1.

Note that the bootstrap variable body-bg works in both versions.

# This shows a red nav bar in bslib 0.5 but not in 0.6.1
library(shiny)
library(bslib)

ui <- page_navbar(
  theme = bs_theme(version = 5, "navbar-bg" = "red"),
  title = "My App",
  nav_panel(title = "One", p("First page content.")),
)

server <- function(...) { }

shinyApp(ui, server)

Start with the supplied Shiny example using bslib 0.6.1, then compare its output with bslib 0.5 and the working body-bg variable. Trace how page_navbar() passes the Bootstrap 5 "navbar-bg" theme variable; done means the example renders a red navbar on 0.6.1 as it does on 0.5.