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

[zkamvar]

Note that this is currently failing because of a typo in episode 12:

processing file: _episodes_rmd/12-supp-factors.Rmd
(*) NOTE: I saw chunk options "reordering-factors, fig. alt = "Bar chart showing control and treatment to emphasise how the function table() tabulates observations.""
 please go to https://yihui.org/knitr/options
 (it is likely that you forgot to quote "character" options)
Error in parse(text = code, keep.source = FALSE) : 
  <text>:1:35: unexpected symbol
1: alist( 'reordering-factors', fig. alt
                                      ^
Calls: source ... parse_params -> withCallingHandlers -> eval -> parse_only -> parse
Execution halted
make: *** [Makefile:131: _episodes/12-supp-factors.md] Error 1

[zkamvar]

NOTE: This will work once #572 is merged.

[tobyhodges]

Merging this to get the workflows running again

[zkamvar]

This is a wonderful surprise! Thank you, Toby!