Bump actions/checkout from 5 to 6 (#115)

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

Author: dependabot[bot]

.github/workflows/typeset.yml

@@ -25,7 +25,7 @@ jobs:
     # Steps represent a sequence of tasks that will be executed as part of the job
     steps:
       - name: Set up Git repository
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
       - name: Compile LaTeX document
         uses: xu-cheng/latex-action@v4
         with:
@@ -64,7 +64,7 @@ jobs:
           sudo apt-get update && sudo apt-get install -y gcc make cpanminus libxslt1-dev libxml-libxml-perl texlive-latex-extra texlive-fonts-recommended
           sudo cpanm --notest LaTeXML
       - name: Set up Git repository
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
       - name: Build site
         run: ./rebuild-site.sh
       - name: Upload split page book site