Fix HTML export test (#12778)

* Fix HTML export test

The masked area changed width deending on the date.

* Mask off more

* Update screenshot

playwright/e2e/chat-export/html-export.spec.ts

@@ -124,7 +124,8 @@ test.describe("HTML Export", () => {
         await expect(page).toMatchScreenshot("html-export.png", {
             mask: [
                 page.getByText("This is the start of export", { exact: false }),
-                page.locator(".mx_DateSeparator_dateHeading"),
+                // We need to mask the whole thing because the width of the time part changes
+                page.locator(".mx_TimelineSeparator"),
                 page.locator(".mx_MessageTimestamp"),
             ],
         });