PPM envvars should take priority

[edavidaja]

in the admittedly unusual circumstance where there is a conflict between the default repo for R sessions and a PACKAGEMANAGER_ADDRESS configured via envvar, I would expect the latter to win:

> options("repos")
$repos
                                         CRAN 
"https://p3m.dev/cran/__linux__/jammy/latest" 

> Sys.getenv("PACKAGEMANAGER_ADDRESS")
[1] "https://colorado.posit.co/rspm"

> ppmtools::list_repos()
  id name hidden
3  2 cran  FALSE

> ppmtools::list_repos(url = "https://colorado.posit.co/rspm")
   id         name hidden
1   4          all  FALSE
4  17 biocran-3.16  FALSE
6  12         cran  FALSE
7   7      curated  FALSE
8   9          dev  FALSE
9   8     internal  FALSE
11 15    published  FALSE
13 10    validated  FALSE