Bump xu-cheng/latex-action from 2 to 3

Bumps [xu-cheng/latex-action](https://github.com/xu-cheng/latex-action) from 2 to 3.
- [Release notes](https://github.com/xu-cheng/latex-action/releases)
- [Commits](xu-cheng/latex-action@v2...v3)

---
updated-dependencies:
- dependency-name: xu-cheng/latex-action
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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

.github/workflows/build_assignments.yml

@@ -38,7 +38,7 @@ jobs:
         uses: actions/download-artifact@v4
 
       - name: Build LaTeX document parts
-        uses: xu-cheng/latex-action@v2
+        uses: xu-cheng/latex-action@v3
         with:
           root_file: ${{ matrix.part }}.tex
           working_directory: sources
@@ -65,7 +65,7 @@ jobs:
             done
 
       - name: Build LaTeX document
-        uses: xu-cheng/latex-action@v2
+        uses: xu-cheng/latex-action@v3
         with:
           root_file: assignments.tex
           working_directory: sources