update_citation() leaves CITATION.cff out of .Rbuildignore

[larnsce]

Observed with washr 1.0.2 and cffr 1.4.1.

update_citation() writes CITATION.cff at the top level but never adds it to .Rbuildignore, and the internal cffr::cff_write() call does not add it either. The next R CMD check then reports:

Non-standard file/directory found at top level: 'CITATION.cff'

washr itself is not affected because it carries no top-level CITATION.cff, but every data package that follows the workflow is.

Fix: add usethis::use_build_ignore("CITATION.cff") inside update_citation() (idempotent, so safe on every run).