Bump actions/checkout from 6 to 7

Bumps [actions/checkout](https://github.com/actions/checkout) from 6 to 7.
- [Release notes](https://github.com/actions/checkout/releases)
- [Changelog](https://github.com/actions/checkout/blob/main/CHANGELOG.md)
- [Commits](actions/checkout@v6...v7)

---
updated-dependencies:
- dependency-name: actions/checkout
  dependency-version: '7'
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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

Author: dependabot[bot]

.github/workflows/build-pdf.yml

@@ -8,7 +8,7 @@ jobs:
    runs-on: ubuntu-latest
    steps:
    - name: Checkout
-     uses: actions/checkout@v6
+     uses: actions/checkout@v7
 
    - name: Run pdflatex
      uses: xu-cheng/texlive-action@v3

.github/workflows/build-website.yml

@@ -8,7 +8,7 @@ jobs:
    runs-on: ubuntu-latest
    steps:
    - name: Checkout
-     uses: actions/checkout@v6
+     uses: actions/checkout@v7
 
    - name: Run make4ht
      uses: docker://ghcr.io/michal-h21/make4ht-action:latest