Only install {survMisc} when calculating test coverage

[jdblischak]

This is a minor follow-up to my previous PR #370 that dealt with the archived package {survMisc} (#359). In that PR I used the Config/Needs strategy to install {survMisc} only in our CI runs. The goal was to continue to run these tests during development while avoiding any problems with CRAN policies.

However, while I had confirmed that {survMisc} was installed, I had missed that the tests were still skipped in the R CMD check workflow. After some troubleshooting both locally and in GitHub Actions, it is my understanding that this is a fundamental limitation of R CMD check, and not a shortcoming of eg r-lib/actions/check-r-package. From what I can tell, R CMD check creates a temporary directory that only contains packages that are explicitly listed in Imports/Suggests/etc. Thus even though {survMisc} was installed, it was not available to {testthat} running inside of R CMD check.

However, since our coverage pipeline directly runs covr::package_coverage(), it does run those tests, which I feel is sufficient. To make it clear that the {survMisc}-related tests are only being run in the coverage workflow, I have updated DESCRIPTION and the workflow files accordingly.

[jdblischak]

{testthat} output in test coverage log showing zero skipped tests:

[ FAIL 0 | WARN 1 | SKIP 0 | PASS 275 ]

[yihui]

From what I can tell, R CMD check creates a temporary directory that only contains packages that are explicitly listed in Imports/Suggests/etc.

Yes, that's true.