Bump actions/checkout from 4 to 6

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>

Author: dependabot[bot]

.github/workflows/hook-dependabot.yml

@@ -17,7 +17,7 @@ jobs:
     env:
       head_ref: ${{ github.event.pull_request.head.ref }}
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
         with:
           ref: ${{ env.head_ref }}
       - uses: DeterminateSystems/nix-installer-action@v19

.github/workflows/test.yml

@@ -12,7 +12,7 @@ jobs:
   test:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
       - uses: DeterminateSystems/determinate-nix-action@v3
         with:
           extra-conf: |

.github/workflows/update-nix.yml

@@ -12,7 +12,7 @@ jobs:
   lockfile:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
       - uses: DeterminateSystems/determinate-nix-action@v3
         with:
           extra-conf: |