databases/R-cran-nanoparquet: Update 0.5.1 => 0.5.2

While here, add required R-cran-testthat to TEST_DEPENDS.

Changelog:
https://cran.r-project.org/web/packages/nanoparquet/news/news.html

PR: 298770
Approved by: osa, vvd (Mentors, implicit)
Signed-off-by: Christos Longros <chris.longros@gmail.com>