Update actions/checkout action to v6 (#9)

Co-authored-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>

Author: renovate[bot]

.github/workflows/publish.yml

@@ -17,7 +17,7 @@ jobs:
     environment:
       name: ${{ github.event.inputs.environment }}
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v6
 
       - name: Set up Python
         uses: actions/setup-python@v3

.github/workflows/test-publish.yml

@@ -17,7 +17,7 @@ jobs:
     environment:
       name: ${{ github.event.inputs.environment }}
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v6
 
       - name: Set up Python
         uses: actions/setup-python@v3