Bump actions/upload-artifact from 5 to 6

Bumps [actions/upload-artifact](https://github.com/actions/upload-artifact) from 5 to 6.
- [Release notes](https://github.com/actions/upload-artifact/releases)
- [Commits](actions/upload-artifact@v5...v6)

---
updated-dependencies:
- dependency-name: actions/upload-artifact
  dependency-version: '6'
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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

Author: dependabot[bot]

.github/workflows/docker-publish.yml

@@ -48,7 +48,7 @@ jobs:
         run: uv build
 
       - name: Upload wheel package
-        uses: actions/upload-artifact@v5
+        uses: actions/upload-artifact@v6
         with:
           name: ${{ runner.os }}-wheel-${{ github.sha }}
           path: dist/wetterdienst-*.whl

.github/workflows/frontend-tests.yml

@@ -213,15 +213,15 @@ jobs:
 
       - name: Upload test results
         if: always()
-        uses: actions/upload-artifact@v4
+        uses: actions/upload-artifact@v6
         with:
           name: playwright-report
           path: frontend/playwright-report/
           retention-days: 7
 
       - name: Upload backend logs
         if: failure()
-        uses: actions/upload-artifact@v4
+        uses: actions/upload-artifact@v6
         with:
           name: backend-logs
           path: backend.log