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/docs.yml

@@ -131,7 +131,7 @@ jobs:
       # Store the docs as a build artifact so we can deploy it later
       - name: Upload HTML documentation as an artifact
         if: github.event_name == 'release' || github.event_name == 'push'
-        uses: actions/upload-artifact@v2
+        uses: actions/upload-artifact@v4
         with:
           name: docs-${{ github.sha }}
           path: doc/_build/html

.github/workflows/pypi.yml

@@ -69,7 +69,7 @@ jobs:
       - name: Upload archives as artifacts
         # Only if not a pull request
         if: success() && github.event_name != 'pull_request'
-        uses: actions/upload-artifact@v2
+        uses: actions/upload-artifact@v4
         with:
           name: pypi-${{ github.sha }}
           path: dist