update upload-artifact action to v4

Author: Sonja Stockhaus

.github/workflows/test.yaml

@@ -59,7 +59,7 @@ jobs:
           pytest -v --cov --color=yes --cov-report=xml
       - name: Archive figures generated during testing
         if: always()
-        uses: actions/upload-artifact@v3
+        uses: actions/upload-artifact@v4
         with:
           name: visual_test_results_${{ matrix.os }}-python${{ matrix.python }}
           path: /home/runner/work/spatialdata-plot/spatialdata-plot/tests/figures/*