fix: Incorrect hovered items in tooltips (#30405)

superset-frontend/plugins/plugin-chart-echarts/src/MixedTimeseries/transformProps.ts

@@ -593,6 +593,7 @@ export default function transformProps(
           extractForecastValuesFromTooltipParams(forecastValue);
 
         const keys = Object.keys(forecastValues);
+        let focusedRow;
         keys.forEach(key => {
           const value = forecastValues[key];
           // if there are no dimensions, key is a verbose name of a metric,
@@ -627,12 +628,11 @@ export default function transformProps(
               : tooltipFormatterSecondary,
           });
           rows.push(row);
+          if (key === focusedSeries) {
+            focusedRow = rows.length - 1;
+          }
         });
-        return tooltipHtml(
-          rows,
-          tooltipFormatter(xValue),
-          keys.findIndex(key => key === focusedSeries),
-        );
+        return tooltipHtml(rows, tooltipFormatter(xValue), focusedRow);
       },
     },
     legend: {