Keep thematic reference years accurate

backend/tests/test_sprint237_flanders_thematic_on_demand.py

@@ -19,6 +19,7 @@ def test_flanders_workspace_exposes_governed_thematic_products_on_demand() -> No
     assert "'Op aanvraag'" in workspace
     assert "theme.id === 'space_occupation'" in workspace
     assert "setActiveThemeId(fallbackTheme.id)" in workspace
+    assert "return `referentiejaar ${observationYear}`" in workspace
     assert "thematicProductKey: thematicProduct.key" in workspace
     assert "datasetsApi.listThematicRasterProducts" in product_hook
     assert "datasetsApi.acquireThematicRaster" in selection_hook