install r for CI

Author: mbostock

.github/workflows/test.yml

@@ -15,6 +15,7 @@ jobs:
         with:
           node-version: 18
           cache: 'yarn'
+      - uses: r-lib/actions/setup-r@v2
       - run: yarn --frozen-lockfile
       - run: yarn test:mocha
       - run: |