Ensure sent markers are hidden when showing thread summary. (#31076)

* Ensure read markers are hidden when showing thread summary.

* lint

* update screenshot

playwright/e2e/threads/threads.spec.ts

@@ -445,7 +445,7 @@ test.describe("Threads", () => {
         await expect(locator.locator(".mx_EventTile").last().getByText("Hello Mr. User")).toBeAttached();
     });
 
-    test("navigate through right panel", async ({ page, app, user }) => {
+    test("navigate through right panel", { tag: "@screenshot" }, async ({ page, app, user }) => {
         // Create room
         const roomId = await app.client.createRoom({});
         await page.goto("/#/room/" + roomId);
@@ -497,6 +497,9 @@ test.describe("Threads", () => {
         await expect(
             threadPanel.locator(".mx_EventTile_last").getByText("Hello again Mr. User in a thread"),
         ).toBeVisible();
+        await expect(threadPanel).toMatchScreenshot("thread-panel.png", {
+            css: ".mx_MessageTimestamp { visibility: hidden !important; }",
+        });
 
         const rightPanel = page.locator(".mx_RightPanel");
         // Check that the threads are listed