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

Author: renovate[bot]

.github/workflows/release.yml

@@ -13,7 +13,7 @@ jobs:
         python-version: ["3.9", "3.10", "3.11", "3.12", "3.13"]
 
     steps:
-    - uses: actions/checkout@v4
+    - uses: actions/checkout@v6
 
     - name: Set up Python ${{ matrix.python-version }}
       uses: actions/setup-python@v5
@@ -37,7 +37,7 @@ jobs:
       id-token: write  # For trusted publishing to PyPI
 
     steps:
-    - uses: actions/checkout@v4
+    - uses: actions/checkout@v6
       with:
         fetch-depth: 0  # Fetch full history for changelog generation