fixed the typo for test argument section of in-line roxygen2 document…

[KimOhn]

…ation

Fix #1985

What changes are proposed in this pull request?
Fixing the typo inside the test argument section of add_p.R roxygen2 in-line documentation (line 71) from Krustkal to Kruskal so that the package reference documentation on the pkgdown website has the correct test name

If there is an GitHub issue associated with this pull request, please provide link.
#1985

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Reviewer Checklist (if item does not apply, mark is as complete)

• PR branch has pulled the most recent updates from main branch.
• If a bug was fixed, a unit test was added.
• Run pkgdown::build_site(). Check the R console for errors, and review the rendered website.
• Code coverage is suitable for any new functions/features: devtools::test_coverage()
• usethis::use_spell_check() runs with no spelling errors in documentation
• All GitHub Action workflows pass with a ✅

When the branch is ready to be merged into master:

• Update NEWS.md with the changes from this pull request under the heading "# gtsummary (development version)". If there is an issue associated with the pull request, reference it in parentheses at the end update (see NEWS.md for examples).
• Increment the version number using usethis::use_version(which = "dev")
• Run usethis::use_spell_check() again
• Approve Pull Request
• Merge the PR. Please use "Squash and merge".

[ddsjoberg]

Thank you @KimOhn !!!