Add Debian with --as-cran to GitHub Actions workflow

Co-authored-by: osorensen <21175639+osorensen@users.noreply.github.com>

Author: Copilot

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

@@ -23,6 +23,8 @@ jobs:
           - {os: ubuntu-latest,   r: 'release'}
           - {os: ubuntu-latest,   r: 'oldrel-1'}
           - {os: windows-latest,  r: 'release'}
+          # Debian-like environment with CRAN checks
+          - {os: ubuntu-latest,   r: 'devel', http-user-agent: 'release', check-as-cran: 'true'}
 
     env:
       GITHUB_PAT: ${{ secrets.GITHUB_TOKEN }}
@@ -48,3 +50,4 @@ jobs:
         with:
           upload-snapshots: true
           build_args: 'c("--no-manual","--compact-vignettes=gs+qpdf")'
+          args: ${{ matrix.config.check-as-cran == 'true' && 'c("--as-cran")' || 'c("--no-manual")' }}