Bump actions/checkout from 5 to 6

Bumps [actions/checkout](https://github.com/actions/checkout) from 5 to 6.
- [Release notes](https://github.com/actions/checkout/releases)
- [Changelog](https://github.com/actions/checkout/blob/main/CHANGELOG.md)
- [Commits](actions/checkout@v5...v6)

---
updated-dependencies:
- dependency-name: actions/checkout
  dependency-version: '6'
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

.github/workflows/tests.yml

@@ -19,7 +19,7 @@ jobs:
       matrix:
         os: [ubuntu-22.04, ubuntu-24.04]
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - name: Install System Python
         run: |
           sudo apt install python3-dev python3-pip python3-venv
@@ -47,7 +47,7 @@ jobs:
         os: [windows-latest, macos-latest, ubuntu-latest]
     steps:
       - name: Checkout project
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
       - name: Install Python
         uses: actions/setup-python@v6
         with:
@@ -73,7 +73,7 @@ jobs:
       matrix:
         os: [ubuntu-latest, windows-latest, macos-latest]
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - uses: conda-incubator/setup-miniconda@v3
         with:
           auto-update-conda: true
@@ -96,7 +96,7 @@ jobs:
     steps:
       - name: Install System Python and Git
         run: yum install -y python3-devel python3-pip python3 git
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - name: Install Testing Requirements
         run: python3 -m pip install nox
       - name: Run Tests
@@ -131,7 +131,7 @@ jobs:
             python:p
             python-pip:p
           update: true
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - name: Run tests
         run: |
           python -m venv .venv
@@ -158,7 +158,7 @@ jobs:
           apk add python3 python3-dev py3-pip py3-nox py3-attrs git
           apk add bash gpg curl
       - name: Download Source
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
       - name: Run Tests
         run: |
           nox -e tests
@@ -176,7 +176,7 @@ jobs:
         run: |
           brew install python git
       - name: Download Source
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
       - name: Build venv
         run: |
           python3 -m venv .venv
@@ -205,7 +205,7 @@ jobs:
         run: |
           pacman --noconfirm -Sy python python-pip git
       - name: Download Source
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
       - name: Create and activate environment
         run: |
           python -m venv .venv