Fix CRAN build

[zachmayer]

https://cran.r-project.org/web/checks/check_results_caretEnsemble.html

Dear maintainer,

Please see the problems shown on https://cran.r-project.org/web/checks/check_results_caretEnsemble.html.

Please correct before 2023-02-12 to safely retain your package on CRAN.

The CRAN Team

[zachmayer]

all the breaking tests are running on r-devel. They all seem to use expect_warning. It seems that predict.lm used to say prediction from a rank-deficient fit may be misleading but no longer gives that warning.

I plan to update the tests to suppress the warnings, but not to expect them