Update actions/checkout to v3 (#41)

Author: RTann

.github/workflows/ci.yml

@@ -15,7 +15,7 @@ jobs:
       - uses: actions/setup-go@v3
         with:
           go-version: 1.16.15
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v3
         with:
           fetch-depth: 1