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

Author: renovate[bot]

.github/workflows/pypi-publish.yml

@@ -11,7 +11,7 @@ jobs:
       id-token: write
     steps:
       - name: Checkout sources
-        uses: actions/checkout@v4
+        uses: actions/checkout@v6
       - uses: actions/setup-python@v5
         with:
           python-version: '3.14'