Bump the actions group with 1 update

Bumps the actions group with 1 update: [actions/upload-artifact](https://github.com/actions/upload-artifact).


Updates `actions/upload-artifact` from 3 to 4
- [Release notes](https://github.com/actions/upload-artifact/releases)
- [Commits](actions/upload-artifact@v3...v4)

---
updated-dependencies:
- dependency-name: actions/upload-artifact
  dependency-type: direct:production
  update-type: version-update:semver-major
  dependency-group: actions
...

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

.github/workflows/docs.yml

@@ -38,7 +38,7 @@ jobs:
           cd docs
           make html SPHINXOPTS="-W"
       - name: Upload HTML
-        uses: actions/upload-artifact@v3
+        uses: actions/upload-artifact@v4
         with:
           name: html
           path: build/sphinx/html
@@ -47,7 +47,7 @@ jobs:
           cd docs
           make latexpdf
       - name: Upload PDF
-        uses: actions/upload-artifact@v3
+        uses: actions/upload-artifact@v4
         with:
           name: pdf
           path: docs/build/latex/nbconvert.pdf