Make percy snapshots for user onboarding more reliable (#9132)

* Make percy snapshots for user onboarding more reliable
* Increase stability of lazy loading test

Co-authored-by: Michael Telatynski <7t3chguy@gmail.com>

src/components/views/dialogs/AppDownloadDialog.tsx

@@ -43,7 +43,11 @@ export const AppDownloadDialog: FC<IDialogProps> = ({ onFinished }: IDialogProps
     const urlFDroid = mobileBuilds?.get("fdroid") ?? fallbackFDroid;
 
     return (
-        <BaseDialog title={_t("Download %(brand)s", { brand })} className="mx_AppDownloadDialog" onFinished={onFinished}>
+        <BaseDialog
+            title={_t("Download %(brand)s", { brand })}
+            className="mx_AppDownloadDialog"
+            fixedWidth
+            onFinished={onFinished}>
             { desktopBuilds?.get("available") && (
                 <div className="mx_AppDownloadDialog_desktop">
                     <Heading size="h3">