build(deps): 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/ci-linux-ros.yml

@@ -23,7 +23,7 @@ jobs:
       CCACHE_DIR: /github/home/.ccache
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
         with:
           submodules: recursive
       - uses: actions/cache@v4

.github/workflows/dockgen.yml

@@ -16,7 +16,7 @@ jobs:
       attestations: write
       id-token: write
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
 
       - uses: astral-sh/setup-uv@v7
       - run: uvx dockgen

.github/workflows/nix.yml

@@ -17,7 +17,7 @@ jobs:
       matrix:
         os: [ubuntu, macos]
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - uses: cachix/install-nix-action@v31
       - uses: cachix/cachix-action@v16
         with: