Bump actions/checkout from 5 to 6 (#166)

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>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

.github/workflows/ci.yml

@@ -17,7 +17,7 @@ jobs:
       ARGO_VM:  ${{ matrix.vm  }}
     steps:
       - name: Checkout code
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
       - name: Install packages
         run: |
           sudo apt-get update

.github/workflows/codespell.yml

@@ -4,5 +4,5 @@ jobs:
   codespell:
     runs-on: ubuntu-latest
     steps:
-    - uses: actions/checkout@v5
+    - uses: actions/checkout@v6
     - uses: codespell-project/actions-codespell@master

.github/workflows/cpplint.yml

@@ -4,7 +4,7 @@ jobs:
   cpplint:
     runs-on: ubuntu-latest
     steps:
-    - uses: actions/checkout@v5
+    - uses: actions/checkout@v6
     - uses: actions/setup-python@v6
     - run: pip install cpplint
     - run: cpplint --quiet --root=../ --filter=-build/c++11,-build/include,-runtime/array,-runtime/string,-whitespace/braces,-whitespace/indent,-whitespace/line_length,-whitespace/tab --recursive src tests