Update actions/checkout action to v6

Author: renovate[bot]

.github/workflows/test.yaml

@@ -10,7 +10,7 @@ jobs:
       matrix:
         go-version: [ '1.19', '1.20']
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
 
       - name: Set up Go
         uses: actions/setup-go@v4