Hello,
I think this might be because the URL for this package is not a CRAN URL: https://svn.r-project.org/R-packages/trunk/foreign
I read in a related post it seems that you can set the URL for alternative repositories (at the top of your script):
options("repos" = c("CRAN" = "https://cran.rstudio.com", "custom" = "file:///path/to/my/mount"))
So probably that should be then:
options("repos" = c("CRAN" = "https://cran.rstudio.com",
"svn.r-project" = "https://svn.r-project.org/R-packages/trunk/foreign"))
I'm not sure if you have to use the full path, or just parts of it like https://svn.r-project.org or https://svn.r-project.org/R-packages or https://svn.r-project.org/R-packages/trunk.
Hope this helps,
PJ