Install missing tex pkg for GH Actions

Author: mwmclean

.github/workflows/R-CMD-check.yaml

@@ -35,6 +35,8 @@ jobs:
 
       - uses: r-lib/actions/setup-tinytex@master
 
+      - run: tlmgr install pdfpages
+
       - uses: r-lib/actions/setup-r@v1
         with:
           r-version: ${{ matrix.config.r }}