Bump actions/checkout from 2 to 5

Bumps [actions/checkout](https://github.com/actions/checkout) from 2 to 5.
- [Release notes](https://github.com/actions/checkout/releases)
- [Changelog](https://github.com/actions/checkout/blob/main/CHANGELOG.md)
- [Commits](actions/checkout@v2...v5)

---
updated-dependencies:
- dependency-name: actions/checkout
  dependency-version: '5'
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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

Author: dependabot[bot]

.github/workflows/main.yml

@@ -22,7 +22,7 @@ jobs:
     steps:
       # Checks-out your repository under $GITHUB_WORKSPACE, so your job can access it
       - name: Set up Git repository
-        uses: actions/checkout@v2
+        uses: actions/checkout@v5
 
       # First run of pdflatex.
       - name: First pdflatex FormalLanguageConstrainedReachabilityLectureNotes