GHA rhub workflow: set bash shell explicitly for options(repos)

Author: florisvdh

.github/workflows/rhub.yaml

@@ -89,6 +89,7 @@ jobs:
         run: |
           # Add additional r-universe repository
           echo 'options(repos = c(getOption("repos"), "https://geocompr.r-universe.dev"))' >> ~/.Rprofile
+        shell: bash
       - uses: r-hub/actions/platform-info@v1
         with:
           token: ${{ secrets.RHUB_TOKEN }}