chore(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.yaml

@@ -72,7 +72,7 @@ jobs:
       eval: ${{ steps.get-attrs.outputs.eval }}
       darwin-hosts: ${{ steps.get-attrs.outputs.darwin-hosts }}
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
         with:
           sparse-checkout: |
             nix/hosts.nix

.github/workflows/update-flakes.yaml

@@ -12,7 +12,7 @@ jobs:
     outputs:
       flake-inputs: ${{ steps.get-flake-inputs.outputs.flake-inputs }}
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
         with:
           sparse-checkout: flake.lock
       - id: get-flake-inputs
@@ -27,7 +27,7 @@ jobs:
       fail-fast: false
       matrix: ${{ fromJson(needs.get-flake-inputs.outputs.flake-inputs) }}
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
         with:
           lfs: false
       - uses: nixbuild/nix-quick-install-action@v34