Bump actions/checkout from 2 to 3 (cabforum#342)

Bumps [actions/checkout](https://github.com/actions/checkout) from 2 to 3.
- [Release notes](https://github.com/actions/checkout/releases)
- [Changelog](https://github.com/actions/checkout/blob/main/CHANGELOG.md)
- [Commits](actions/checkout@v2...v3)

---
updated-dependencies:
- dependency-name: actions/checkout
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

.github/workflows/build-draft-docs.yml

@@ -12,10 +12,10 @@ jobs:
     runs-on: ubuntu-20.04
     steps:
       - name: Checkout the code
-        uses: actions/checkout@v2
+        uses: actions/checkout@v3
       - name: Checkout old version for redline
         if: ${{ github.event_name == 'pull_request' || github.event_name == 'push' }}
-        uses: actions/checkout@v2
+        uses: actions/checkout@v3
         with:
           ref: ${{ github.event.pull_request.base.sha || github.event.push.before }}
           path: old/