chore(deps): update actions/checkout action to v6

Author: renovate[bot]

.github/workflows/ci.yml

@@ -17,7 +17,7 @@ jobs:
         go: [ 'oldstable', 'stable' ]
 
     steps:
-    - uses: actions/checkout@v4
+    - uses: actions/checkout@v6
 
     - uses: actions/setup-go@v6
       with:
@@ -36,6 +36,6 @@ jobs:
     runs-on: ubuntu-latest
 
     steps:
-    - uses: actions/checkout@v4
+    - uses: actions/checkout@v6
 
     - uses: fsfe/reuse-action@v6