build(deps): bump actions/checkout from 3 to 6

Bumps [actions/checkout](https://github.com/actions/checkout) from 3 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/v3...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/test.yml

@@ -16,7 +16,7 @@ jobs:
             runner: ubuntu-24.04-arm
     runs-on: ${{ matrix.runner }}
     steps:
-    - uses: actions/checkout@v3
+    - uses: actions/checkout@v6
       with:
         fetch-depth: 0
     - uses: cachix/install-nix-action@v31

.github/workflows/update-flakes.yml

@@ -11,7 +11,7 @@ jobs:
       contents: write
       pull-requests: write
     steps:
-    - uses: actions/checkout@v3
+    - uses: actions/checkout@v6
     - uses: cachix/install-nix-action@v31
     - name: Update flake inputs
       run: nix flake update