allow installing R 4 via Conda

[palday]

closes #497

CI failure seems to be: JuliaLang/julia#50611

[codecov]

Codecov Report

Patch and project coverage have no change.

Comparison is base (305efff) 75.16% compared to head (4349653) 75.16%.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #498   +/-   ##
=======================================
  Coverage   75.16%   75.16%           
=======================================
  Files          25       25           
  Lines        1623     1623           
=======================================
  Hits         1220     1220           
  Misses        403      403           

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[PallHaraldsson]

I'm a bit surprised this wasn't possible before, with R 4.0 quite old. Does it simply mean that People used 4.x e.g. 4.3 before, just preinstalled, not using Conda? I.e. the Conda option no used much, or any other reason delaying adding support for R 4 with it?

Since it's possible to use Conda to install, has it been thought about to have it as an auto-install option?

[palday]

@PallHaraldsson R is automatically installed via Conda if system R isn't found. All of this is documented: https://juliainterop.github.io/RCall.jl/stable/installation/

Also, this change was only for the auto-install via Conda. Previously, R could be whatever you wanted as long as you installed it yourself. For example, I've regularly used RCall with R 4.3 for a while now.