fix(ci): drop unused google-chrome apt source before setup-r

r-lib/actions/setup-r@v2 runs `sudo apt-get update` before installing
R, which fails outright if any configured apt source is broken - even
one we never touch. The google-chrome source baked into GitHub's
ubuntu-latest image intermittently serves a stale Packages.gz that
doesn't match its own Release file's hash (a Google CDN sync race),
which took down every Linux leg of the R-CMD-check matrix on
2026-09-09 regardless of R version. Removing the source we don't need
makes this failure class impossible here.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

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

@@ -44,6 +44,18 @@ jobs:
 
       - uses: r-lib/actions/setup-pandoc@v2
 
+      - name: Drop the unused google-chrome apt source
+        if: runner.os == 'Linux'
+        run: sudo rm -f /etc/apt/sources.list.d/google-chrome.list
+        # setup-r@v2 runs `sudo apt-get update` before installing R, and that
+        # command fails outright if ANY configured apt source is broken --
+        # even one we never use. The google-chrome source baked into GitHub's
+        # ubuntu-latest image intermittently serves a stale Packages.gz that
+        # doesn't match its own Release file's hash (a Google CDN sync race,
+        # not anything about R or this repo), which took down every ubuntu
+        # leg of this matrix on 2026-09-09. Removing the source we don't need
+        # makes that whole failure class impossible here.
+
       - uses: r-lib/actions/setup-r@v2
         with:
           r-version: ${{ matrix.config.r }}