Recognize P3M packages as CRAN packages, on macOS as well

``` getOption("repos") #> P3M CRAN #> "https://p3m.dev/cran/latest" "https://cloud.r-project.org/" ``` Packages installed from P3M are constantly reinstalled, because they are not considered to be CRAN packages. There is a slight chance that the package to be installed need to be loaded (e.g. from `.Rprofile`).