Bump actions/upload-artifact from 3 to 4

Bumps [actions/upload-artifact](https://github.com/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
...

Signed-off-by: dependabot[bot] <[email protected]>

.github/workflows/tests.yml

@@ -104,14 +104,14 @@ jobs:
 
       - name: Upload coverage data
         if: always() && matrix.session == 'tests'
-        uses: "actions/upload-artifact@v3"
+        uses: "actions/upload-artifact@v4"
         with:
           name: coverage-data
           path: ".coverage.*"
 
       - name: Upload documentation
         if: matrix.session == 'docs-build'
-        uses: actions/upload-artifact@v3
+        uses: actions/upload-artifact@v4
         with:
           name: docs
           path: docs/_build