deps(actions)(deps): bump actions/checkout from 4 to 6 (#73)

Bumps [actions/checkout](https://github.com/actions/checkout) from 4 to 6.
- [Release notes](https://github.com/actions/checkout/releases)
- [Changelog](https://github.com/actions/checkout/blob/main/CHANGELOG.md)
- [Commits](actions/checkout@v4...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/build-upstream-besu.yml

@@ -18,7 +18,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout repository
-        uses: actions/checkout@v4
+        uses: actions/checkout@v6
 
       - name: Dotenv Action
         id: dotenv
@@ -42,7 +42,7 @@ jobs:
             core.setFailed('Release tag ${{ steps.dotenv.outputs.linea_besu_version }} already exists in current repository')
 
       - name: Checkout Besu repository
-        uses: actions/checkout@v4
+        uses: actions/checkout@v6
         with:
           repository: hyperledger/besu
           ref: ${{ steps.dotenv.outputs.upstream_besu_ref }}