Function from ggh4x not recognized in R package even though it was imported

Question

I'm trying to build a package which contains a number of plotting functions, primarily based on ggplot2, which also uses guide_axis_minor from ggh4x. I import ggplot2 in total, since my code uses many of its functions, and import specifically the guide_axis_minor function from ggh4x, however when I run check() (specifically the part where it tests examples) I get the following error:

Error in get(as.character(FUN), mode = "function", envir = envir) : 
    object 'guide_axis_minor' of mode 'function' was not found

I built a small test package which reproduces the issue using one function called plot. Here is the code for that function:

#' Plot
#'
#' @param data
#'
#' @return
#' @export
#' @import ggplot2
#' @importFrom ggh4x guide_axis_minor
#'
#' @examples
#' plot(data.frame(x = 1:10, y = 1:10))
plot <- function(data){
  ggplot(data, aes(x, y)) +
    geom_line() +
    scale_y_continuous(guide = 'axis_minor')
}

Here is my DESCRIPTION file:

Package: test
Title: What the Package Does (One Line, Title Case)
Version: 0.0.0.9000
Authors@R: 
    person("First", "Last", , "[email protected]", role = c("aut", "cre"),
           comment = c(ORCID = "YOUR-ORCID-ID"))
Description: What the package does (one paragraph).
License: `use_mit_license()`, `use_gpl3_license()` or friends to pick a
    license
Encoding: UTF-8
Roxygen: list(markdown = TRUE)
RoxygenNote: 7.3.1
Imports: 
    ggh4x,
    ggplot2

And here is my NAMESPACE file:

# Generated by roxygen2: do not edit by hand

export(plot)
import(ggplot2)
importFrom(ggh4x,guide_axis_minor)

If more information about the package would help, I'll be happy to provide it. What am I doing wrong?