ftp/R-cran-curl: Update to 0.6.1

Remove R-cran-magrittr from TEST_DEPENDS.
Add TESTING_UNSAFE=yes:

• checking running R code from vignettes ... 'intro.Rmd' using 'UTF-8'... failed 'windows.Rmd' using 'UTF-8'... OK ERROR

Errors in running code in vignettes:
when running code in 'intro.Rmd'

...

mirros <- read.csv("mirrors.csv")

unlink("mirrors.csv")

close(con)

When sourcing 'intro.R':

Error: invalid connection
Execution halted

PR: 282908