Bump actions/checkout from 5 to 6 in the actions-deps group

Bumps the actions-deps group with 1 update: [actions/checkout](https://github.com/actions/checkout).


Updates `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
  dependency-group: actions-deps
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

.github/workflows/ci.yml

@@ -11,7 +11,7 @@ jobs:
     name: Run all checks
     runs-on: ubuntu-24.04
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - uses: DeterminateSystems/determinate-nix-action@v3
       - uses: DeterminateSystems/flakehub-cache-action@main
 

.github/workflows/update-downstream.yml

@@ -40,7 +40,7 @@ jobs:
       GH_TOKEN: ${{ secrets.detsys_pr_bot_token }} # for `gh pr create`
     steps:
       - name: Check out detsys-ts
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
         with:
           path: current
           token: ${{ env.GH_TOKEN }}
@@ -53,7 +53,7 @@ jobs:
           echo "msg=${MSG}" >> $GITHUB_OUTPUT
 
       - name: Check out ${{ env.TARGET_REPO }}
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
         with:
           path: target
           repository: ${{ env.TARGET_REPO }}