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

Author: renovate[bot]

.github/workflows/ci.yaml

@@ -21,7 +21,7 @@ jobs:
         python-version: ["3.11"]
 
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - name: Set up Python ${{ matrix.python-version }}
         uses: actions/setup-python@v6
         with:
@@ -47,7 +47,7 @@ jobs:
       # with sigstore/fulcio when running outside of PRs.
       id-token: write
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - name: Login GHCR
         uses: docker/login-action@v3
         with: