fix: Set result chart burst Y axis max after adding PB line (@Ed-k) (monkeytypegame#6980)

### Description

The result chart burst axis maximum Y value needs to be updated after
adding the personal best line to keep the chart scale the same as the
wpm and raw lines.

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Closes #
monkeytypegame#6979

Author: Ed-k

frontend/src/ts/test/result.ts

@@ -352,6 +352,7 @@ export async function updateGraphPBLine(): Promise<void> {
 
   ChartController.result.getScale("wpm").max = maxChartVal;
   ChartController.result.getScale("raw").max = maxChartVal;
+  ChartController.result.getScale("burst").max = maxChartVal;
 }
 
 function updateWpmAndAcc(): void {