Update `is.waive` to `is.waiver`

[donyunardi]

Hello,

ggplot's is.waive is not exported and renamed to is.waiver:
tidyverse/ggplot2#6173

This update was done in Nov 2024 and will be available on the next release.

Probably need to update these lines:

ggmosaic/R/utilities.R

Line 55 in 5dc7ef9

is.waive <- getFromNamespace("is.waive", "ggplot2")

ggmosaic/R/scale-product.R

Line 37 in 5dc7ef9

if (!is.waive(sec.axis)) {

Let me know if you agree and I can raise a PR.