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>

Author: dependabot[bot]

.github/workflows/ci.yml

@@ -97,7 +97,7 @@ jobs:
           COVERAGE_FILE: .coverage.${{ matrix.python-version }}
 
       - name: Upload coverage data
-        uses: actions/upload-artifact@v4
+        uses: actions/upload-artifact@v6
         with:
           name: coverage-data-${{ matrix.python-version }}
           path: .coverage.${{ matrix.python-version }}
@@ -125,7 +125,7 @@ jobs:
           python -m coverage html --skip-covered --skip-empty
           python -m coverage report --fail-under=70
       - name: Upload HTML report
-        uses: actions/upload-artifact@v4
+        uses: actions/upload-artifact@v6
         with:
           name: html-report
           path: htmlcov