install r on ubuntu runners

this was removed in ubuntu-24.04 github actions runner

Author: asottile

.github/workflows/languages.yaml

@@ -65,6 +65,8 @@ jobs:
       if: matrix.os == 'windows-latest' && matrix.language == 'perl'
     - uses: haskell/actions/setup@v2
       if: matrix.language == 'haskell'
+    - uses: r-lib/actions/setup-r@v2
+      if: matrix.os == 'ubuntu-latest' && matrix.language == 'r'
 
     - name: install deps
       run: python -mpip install -e . -r requirements-dev.txt