Update tests for upcoming ggplot2 change

[teunbrand]

Hi there,

While preparing for a new release of ggplot2 and during a reverse dependency check, it became apparent that the prospective ggplot2 3.5.0 would break breakDown.

This PR updates a test that implicitly expects the length of ggplot objects to be 9. With the new version, this no longer holds true. Instead the tests expect the plot to be of the same length as a ggplot object.

To test the code changes with the release candidate, you can install it with the code below:

remotes::install_github("tidyverse/ggplot2", ref = remotes::github_pull("5592"))

The release of ggplot2 3.5.0 is scheduled for the 12th of Februari. The progress of the release can be tracked in tidyverse/ggplot2#5588. We hope that this PR might help breakDown get out a fix if necessary.

[teunbrand]

This is just a kind reminder that the release is scheduled soon.

[pbiecek]

thanks