dont run install test that relies on latest release not being RC

Author: rok-cesnovar

tests/testthat/test-install.R

@@ -30,6 +30,7 @@ test_that("install_cmdstan() successfully installs cmdstan", {
 test_that("install_cmdstan() errors if installation already exists", {
   skip_if_offline()
   skip_on_cran()
+  skip_if(grepl("rc.+$", cmdstanr::cmdstan_path()))
   if (not_on_cran()) {
     # want to test passing NULL to install_cmdstan but need a real dir to
     # check in dir.exists() below so also create dir_check