chore: update actions/checkout action to v6

Author: renovate[bot]

.github/workflows/publish.yml

@@ -14,7 +14,7 @@ jobs:
     runs-on: ubuntu-latest
 
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
 
       - name: Set up Python
         uses: astral-sh/setup-uv@v6

.github/workflows/python-test.yml

@@ -20,7 +20,7 @@ jobs:
         python-version: ["3.11", "3.12"]
 
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
 
       - name: Set up Python
         uses: astral-sh/setup-uv@v6