update github action checkout to v6

Author: LostInDarkMath

.github/workflows/main.yml

@@ -12,7 +12,7 @@ jobs:
     runs-on: ubuntu-latest
 
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
         with:
           fetch-depth: 0  # we need history to diff properly
 
@@ -52,7 +52,7 @@ jobs:
         python-version: [3.11, 3.12, 3.13, 3.14]
 
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
 
       - name: Set up Python ${{ matrix.python-version }}
         uses: actions/setup-python@v5
@@ -84,7 +84,7 @@ jobs:
     environment:
       name: pypi-deployment
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
 
       - name: Set up Python
         uses: actions/setup-python@v5