try installing miniconda first

Author: cpsievert

.github/workflows/R-CMD-check.yaml

@@ -103,6 +103,7 @@ jobs:
         if: matrix.config.visual_tests == true
         run: |
           sudo chown -R $UID $CONDA
+          Rscript -e "reticulate::install_miniconda()"
           Rscript -e "reticulate::conda_install('visual-testing', 'python-kaleido')"
           Rscript -e "reticulate::use_condaenv('visual-testing')"
           Rscript -e "reticulate::py_config()"