use checkouts v2 to fix issue when rerunning jobs

Author: dfalbel

.github/workflows/main.yaml

@@ -28,7 +28,7 @@ jobs:
       CRAN: ${{ matrix.cran }}
 
     steps:
-      - uses: actions/checkout@v1
+      - uses: actions/checkout@v2
       - uses: r-lib/actions/setup-r@master
       - uses: r-lib/actions/setup-pandoc@master
       - name: Install system dependencies