Check for any incompatibilities with R 4.1.2

[jashapiro]

Implementing #510 resulted in the creation of a new docker image version, which will be used for future builds of training materials. While this will implicitly be tested when we tackle #509, we might want to do that test sooner by rebuilding these materials with the make-live action.

We should also test the exercise notebooks with the unsolve action in that repository.

[jashapiro]

This is closed by #517