Update r-lib/actions/setup-r to v2

Author: hhoeflin

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

@@ -41,7 +41,7 @@ jobs:
     steps:
       - uses: actions/checkout@v2
 
-      - uses: r-lib/actions/setup-r@v1
+      - uses: r-lib/actions/setup-r@v2
         id: install-r
         with:
           r-version: ${{ matrix.config.r }}