urgent: fix workflows

[zkamvar]

This pull request updates the workflows for this lesson.

There are two items that are changed:

1. r-lib/actions/setup-r now uses @v2 instead of @master as the default tag
2. the set-output GHA workflow command has been updated as it was deprecated.

see https://github.com/carpentries/styles/issues/641 for details

If you have any questions, contact @zkamvar

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[jcolomb]

checking this