Bump actions/upload-artifact from 2 to 4

Bumps [actions/upload-artifact](https://github.com/actions/upload-artifact) from 2 to 4.
- [Release notes](https://github.com/actions/upload-artifact/releases)
- [Commits](actions/upload-artifact@v2...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/benchmark_pr.yml

@@ -49,7 +49,7 @@ jobs:
                 mkdir -p plots
                 benchpkgplot ${{ steps.extract-package-name.outputs.package_name }} --rev="${{github.event.repository.default_branch}},${{github.event.pull_request.head.sha}}" --npart=10 --format=png --input-dir=results/ --output-dir=plots/
             - name: Upload plot as artifact
-              uses: actions/upload-artifact@v2
+              uses: actions/upload-artifact@v4
               with:
                 name: plots
                 path: plots