Update actions/checkout action to v6

Author: renovate[bot]

.github/workflows/publish_to_pypi.yml

@@ -16,7 +16,7 @@ jobs:
       id-token: write
     steps:
     - name: Checkout code
-      uses: actions/checkout@v5
+      uses: actions/checkout@v6
 
     - name: Set up Python 3.10
       uses: actions/setup-python@v6

.github/workflows/run_test.yml

@@ -18,7 +18,7 @@ jobs:
 
     steps:
     - name: Checkout code
-      uses: actions/checkout@v5
+      uses: actions/checkout@v6
 
     - name: Set up Python
       uses: actions/setup-python@v6