lint-md: make sure to use Rscript

Author: aitap

.github/workflows/code-quality.yaml

@@ -73,4 +73,4 @@ jobs:
       - uses: actions/checkout@v4
       - uses: r-lib/actions/setup-r@v2
       - name: Lint
-        run: .ci/lint.R .ci/linters/md . '[.]R?md$'
+        run: Rscript .ci/lint.R .ci/linters/md . '[.]R?md$'