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] <support@github.com>

Author: dependabot[bot]

.github/workflows/classroom.yml

@@ -16,5 +16,5 @@ jobs:
         with:
           distribution: 'temurin'
           java-version: '24'
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - uses: education/autograding@v1

.github/workflows/feedback.yaml

@@ -28,7 +28,7 @@ jobs:
       SYSTEM_PROMPT: ${{ vars.SYSTEM_PROMPT }}
     steps:
       - name: Checkout repository
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
 
       - name: Read assignment instructions
         id: instructions