Bump actions/checkout from 3 to 4

Bumps [actions/checkout](https://github.com/actions/checkout) from 3 to 4.
- [Release notes](https://github.com/actions/checkout/releases)
- [Changelog](https://github.com/actions/checkout/blob/main/CHANGELOG.md)
- [Commits](actions/checkout@v3...v4)

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

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

.github/workflows/build.yml

@@ -15,7 +15,7 @@ jobs:
     name: "Build on Ubuntu Focal"
     runs-on: ubuntu-20.04
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
       - uses: ros-tooling/setup-ros@v0.6
         with:
           required-ros-distributions: foxy
@@ -30,7 +30,7 @@ jobs:
       matrix:
         ros2_distro: [humble, rolling]
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
       - uses: ros-tooling/setup-ros@v0.6
         with:
           required-ros-distributions: ${{ matrix.ros2_distro }}