Update actions/checkout action to v6

Author: renovate[bot]

.github/workflows/add-header.yml

@@ -11,7 +11,7 @@ jobs:
     name: Add headers
     runs-on: ubuntu-latest
     steps:
-    - uses: actions/checkout@v5
+    - uses: actions/checkout@v6
       with:
         token: ${{ secrets.PAT }}
 

.github/workflows/lint-and-test.yml

@@ -18,7 +18,7 @@ jobs:
     name: Unit tests & coverage
     runs-on: ubuntu-latest
     steps:
-    - uses: actions/checkout@v5
+    - uses: actions/checkout@v6
 
     - name: Set up Python
       uses: actions/setup-python@v6
@@ -46,7 +46,7 @@ jobs:
     name: Integration tests 
     runs-on: ubuntu-latest
     steps:
-    - uses: actions/checkout@v5
+    - uses: actions/checkout@v6
 
     - name: Set up Docker Buildx
       uses: docker/setup-buildx-action@v3

.github/workflows/update-main-version.yml

@@ -20,7 +20,7 @@ jobs:
     permissions:
       contents: write
     steps:
-    - uses: actions/checkout@v5
+    - uses: actions/checkout@v6
       with:
         fetch-depth: 0
     - name: Git config