GHA rhub workflow: change add. repo approach in other platforms *

I mistakenly assumed the setup-r action was the one from r-lib, but it's
rhub's and that one doesn't have the extra_repositories setting.

So replacing this with an options(repos =) statement.

.github/workflows/rhub.yaml

@@ -81,7 +81,11 @@ jobs:
         with:
           job-config: ${{ matrix.config.job-config }}
           token: ${{ secrets.RHUB_TOKEN }}
-          extra-repositories: https://geocompr.r-universe.dev
+      - name: Add additional r-universe repository
+        run: |
+          # Add additional r-universe repository
+          options(repos = c(getOption("repos"), "https://geocompr.r-universe.dev"))
+        shell: Rscript {0}
       - uses: r-hub/actions/platform-info@v1
         with:
           token: ${{ secrets.RHUB_TOKEN }}