github-actions: bump actions/checkout from 6.0.3 to 7.0.0

Bumps [actions/checkout](https://github.com/actions/checkout) from 6.0.3 to 7.0.0.
- [Release notes](https://github.com/actions/checkout/releases)
- [Changelog](https://github.com/actions/checkout/blob/main/CHANGELOG.md)
- [Commits](actions/checkout@df4cb1c...9c091bb)

---
updated-dependencies:
- dependency-name: actions/checkout
  dependency-version: 7.0.0
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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

Author: dependabot[bot]

.github/workflows/build.yml

@@ -48,7 +48,7 @@ jobs:
           tar xjf gcc-arm.tar.bz2
           echo "PATH=/tmp/gcc-arm-none-eabi-9-2019-q4-major/bin:$PATH" >> "$GITHUB_ENV"
       - name: Checkout
-        uses: actions/checkout@df4cb1c069e1874edd31b4311f1884172cec0e10 # v6.0.3
+        uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0 # v7.0.0
         with:
           submodules: recursive
       - name: Build nrf52840 reference release for 1.2