ci: update checkout action

Author: dshemetov

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

@@ -19,7 +19,7 @@ jobs:
       GITHUB_PAT: ${{ secrets.GITHUB_TOKEN }}
       R_KEEP_PKG_SOURCE: yes
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
 
       - uses: r-lib/actions/setup-r@v2
         with: