Fix test for upcoming ggplot2 update

[teunbrand]

Hello there,

We have been preparing a new release of ggplot2 and during a reverse dependency check, it became apparent that the prospective ggplot2 3.5.0 would break shinipsum.

Briefly, testing that the length of a ggplot object is length 9 is brittle for changes in ggplot2 itself. This PR updates the expectation of the test to the lame length as a ggplot object, rather than exactly 9.

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 February. The progress of the release can be tracked in tidyverse/ggplot2#5588. We hope that this PR might help shinipsum get out a fix if necessary.

[teunbrand]

This is a kind reminder that the release of ggplot2 is scheduled soon.

[ColinFay]

Thanks a lot ! will send to CRAN :)