MNT - Fix R installation in CI (#310)

Author: mathurinm

.github/workflows/main.yml

@@ -17,14 +17,17 @@ jobs:
       uses: actions/setup-python@v3
       with:
         python-version: "3.10"
+    - name: Set up R
+      uses: r-lib/actions/setup-r@v2
     - name: Install package and testing tools
       run: |
         python -m pip install --upgrade pip
         pip install .
         pip install .[test]
+        python --version
     - name: Install other dependencies
       run: |
-        conda install rpy2 -c conda-forge
+        pip install rpy2
         pip install statsmodels cvxopt
         pip install sortedl1
         # for testing Cox estimator