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](https://github.com/actions/checkout/compare/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>

.github/workflows/ci.yml

@@ -15,7 +15,7 @@ jobs:
       servers: ${{ steps.servers.outputs.servers }}
       workstations: ${{ steps.workstations.outputs.workstations }}
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - uses: cachix/install-nix-action@v31
         with:
           extra_nix_config: experimental-features = nix-command flakes pipe-operators
@@ -56,7 +56,7 @@ jobs:
       matrix:
         package: ${{ fromJson(needs.parse-flake.outputs.packages) }}
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - uses: cachix/install-nix-action@v31
         with:
           extra_nix_config: experimental-features = nix-command flakes pipe-operators
@@ -76,7 +76,7 @@ jobs:
       matrix:
         check: ${{ fromJson(needs.parse-flake.outputs.checks) }}
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - uses: cachix/install-nix-action@v31
         with:
           extra_nix_config: experimental-features = nix-command flakes pipe-operators
@@ -108,7 +108,7 @@ jobs:
     permissions:
       contents: write
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - name: Push to deploy branch
         run: git push --force origin HEAD:refs/heads/deploy
   await-deploy: