Update actions/checkout action to v3

Author: renovate-bot

.github/workflows/ci.yml

@@ -15,7 +15,7 @@ jobs:
     runs-on: ${{ matrix.os }}
 
     steps:
-    - uses: actions/checkout@v2
+    - uses: actions/checkout@v3
     - uses: UziTech/action-setup-atom@v2
       with:
         version: stable