feat: enable running `testthat::test_local()`/`devtools::test()` independently outside of R CMD check

[cjyetman]

Some (admittedly strange) tests need to be skipped when run in the context of R CMD check, e.g. a test that checks against data in data-raw/ which is not available during R CMD check, so it would be useful to trigger a testthat::test_local()/devtools::test() on its own so that those test are also run in CI.

@jdhoffa @jacobvjk

example tests:
https://github.com/RMI-PACTA/pacta.portfolio.utils/blob/4fd21e5a903c401a3d8af6e2f318295807989b44/tests/testthat/test-quit_if_no_pacta_relevant_data.R#L20-L94

[jdhoffa]

That makes sense!