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](https://github.com/actions/checkout/compare/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>

.github/workflows/1-copilot-extension.yml

@@ -29,7 +29,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
       - id: get_step
         run: echo "current_step=$(cat ./.github/steps/-step.txt)" >> $GITHUB_OUTPUT
     outputs:
@@ -51,7 +51,7 @@ jobs:
     steps:
       # We'll need to check out the repository so that we can edit the README.
       - name: Checkout
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
 
       # Verify the learner added the file contents.
       - name: Check workflow contents, jobs