test: First try with gitlab-ci

- Add automatic test for `R CMD build`
- Add automatic test for `R CMD check` with `NOT_CRAN` set to `true`

Refs #52
4 jobs for 52-implement-automatic-tests-in-the-package in 1 minute and 48 seconds (queued for 1 second)
Status Name Job ID Coverage
  Build
passed build #91891

00:00:28

failed build #91890

00:00:23

failed build #91888

00:00:19

 
  Tests
passed check_not_cran #91889

00:01:20