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] <support@github.com>

.github/workflows/ci-tests.yaml

@@ -100,9 +100,9 @@ jobs:
       - name: "Run tests via Tox"
         run: python -m tox
       - name: "Upload coverage report for unit tests"
-        uses: actions/upload-artifact@v3
+        uses: actions/upload-artifact@v4
         with:
-          name: ${{ format('py{0}-unit-tests', matrix.python) }}
+          name: ${{ format('{0}-py{1}-unit-tests', matrix.on, matrix.python) }}
           path: ./coverage.xml
           retention-days: 1
           if-no-files-found: error
@@ -113,7 +113,7 @@ jobs:
     steps:
       - uses: actions/checkout@v4
       - name: "Download artifacts"
-        uses: actions/download-artifact@v3
+        uses: actions/download-artifact@v4
       - name: "Upload coverage to Codecov"
         uses: codecov/codecov-action@v3
         with: