Update actions/checkout action to v4

Author: renovate[bot]

.github/workflows/main.yaml

@@ -9,7 +9,7 @@ jobs:
     if: "!contains(github.event.head_commit.message, '[ci skip]')"
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v4
       - uses: actions/setup-node@v2
         with:
           node-version: 14