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

Author: renovate[bot]

.github/workflows/ci.yml

@@ -5,7 +5,7 @@ jobs:
   pre-commit:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
       - uses: actions/setup-python@v6
         with:
           python-version: "3.10"
@@ -20,7 +20,7 @@ jobs:
       matrix:
         python-version: ["3.10", "3.12", "3.13"]
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
       - name: Set up Python ${{ matrix.python-version }}
         uses: actions/setup-python@v6
         with:
@@ -41,7 +41,7 @@ jobs:
       matrix:
         version: ["3.10", "3.12", "3.13"]
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
       - uses: actions/setup-python@v6
         with:
           python-version: ${{ matrix.version }}
@@ -71,7 +71,7 @@ jobs:
     runs-on: ${{ matrix.os }}
     steps:
       - name: Checkout repo
-        uses: actions/checkout@v4
+        uses: actions/checkout@v6
 
       - name: Set up Python ${{ matrix.python-version }}
         uses: actions/setup-python@v6
@@ -91,7 +91,7 @@ jobs:
     timeout-minutes: 10
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - name: Convert ipynb to markdown
         shell: bash
         run: |
@@ -108,7 +108,7 @@ jobs:
   build-test:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
 
       - name: Set up Python
         uses: actions/setup-python@v6
@@ -138,7 +138,7 @@ jobs:
   doc-build-test:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
 
       - name: Set up Python
         uses: actions/setup-python@v6

.github/workflows/deploy_doc.yml

@@ -33,7 +33,7 @@ jobs:
               echo "REF=release/$last_minor_version" >> $GITHUB_ENV
           fi
 
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
         with:
           ref: ${{ env.REF }} # checked out branch
 

.github/workflows/pre_release.yml

@@ -21,7 +21,7 @@ jobs:
 
     steps:
       - name: Checkout target branch
-        uses: actions/checkout@v4
+        uses: actions/checkout@v6
         with:
           ref: ${{ github.event.inputs.target_branch }}
           token: ${{ secrets.RELEASE_BOT_PAT }}   # <<< service PAT

.github/workflows/release.yml

@@ -11,7 +11,7 @@ jobs:
       # needed to publish to PyPI
       id-token: write
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
 
       - name: Set up Python
         uses: actions/setup-python@v5