Fix exported png got different backgrounds based on screen density (#46769)

frontend/src/metabase/visualizations/lib/save-chart-image.ts

@@ -28,6 +28,7 @@ export const saveChartImage = async (selector: string, fileName: string) => {
 
   const { default: html2canvas } = await import("html2canvas-pro");
   const canvas = await html2canvas(node, {
+    scale: 2,
     useCORS: true,
     onclone: (doc: Document, node: HTMLElement) => {
       node.classList.add(SAVING_DOM_IMAGE_CLASS);