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/CI.yml

@@ -31,7 +31,7 @@ jobs:
         arch:
           - x64
     steps:
-      - uses: actions/checkout@v6
+      - uses: actions/checkout@v7
       - name: Install FFmpeg
         run: sudo apt-get update && sudo apt-get install -y ffmpeg
       - name: Install XVFB
@@ -70,7 +70,7 @@ jobs:
       statuses: write
       pages: write
     steps:
-      - uses: actions/checkout@v6
+      - uses: actions/checkout@v7
       - name: Install FFmpeg and XVFB
         run: sudo apt-get update && sudo apt-get install -y ffmpeg xvfb
       - uses: actions/setup-python@v6

.github/workflows/draft-pdf.yml

@@ -16,7 +16,7 @@ jobs:
     name: Paper Draft
     steps:
       - name: Checkout
-        uses: actions/checkout@v6
+        uses: actions/checkout@v7
 
       - name: Build draft PDF
         uses: openjournals/openjournals-draft-action@master