use_condaenv does not change actual env

[latot]

Hi, this issue is based on a behavior of use_condaenv, which is probable to happens even if #1587 is fixed.

When we use use_condaenv, instead change the actual env, it appends to PATH the new env, which causes the next:

reticulate::use_condaenv("base")
reticulate::use_condaenv("base")
Sys.getenv("PATH")
[1] "/home/pipe/.local/share/r-miniconda/condabin:/home/pipe/.local/share/r-miniconda/bin:/home/pipe/.local/share/r-miniconda/condabin:/home/pipe/.local/share/r-miniconda/bin:/home/pipe/miniconda3/condabin:/usr/local/sbin:/usr/local/bin:/usr/bin:/opt/bin:/usr/lib/llvm/17/bin"

Now, there is the base paths repeated twice, instead of one time, at the same time, if we change from one env to other, it should not only append a new path to PATH, it should remove from PATH the actual env paths.

Thx.