better to follow the good practice in 26.3.3 Common use cases (#1493)

iteration.qmd

@@ -310,7 +310,8 @@ summarize_means <- function(df, summary_vars = where(is.numeric)) {
   df |> 
     summarize(
       across({{ summary_vars }}, \(x) mean(x, na.rm = TRUE)),
-      n = n()
+      n = n(),
+      .groups = "drop"
     )
 }
 diamonds |>