added windows to GH actions

Author: osorensen

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

@@ -22,6 +22,7 @@ jobs:
           - {os: ubuntu-latest,   r: 'devel', http-user-agent: 'release'}
           - {os: ubuntu-latest,   r: 'release'}
           - {os: ubuntu-latest,   r: 'oldrel-1'}
+          - {os: windows-latest,  r: 'release'}
 
     env:
       GITHUB_PAT: ${{ secrets.GITHUB_TOKEN }}