Hide scroll to bottom button in pinned message e2e test (#28255)

* Hide scroll to bottom button in pinned message e2e test

* Remove redundant mask

* Update playwright/e2e/pinned-messages/pinned-messages.spec.ts

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

---------

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

playwright/e2e/pinned-messages/pinned-messages.spec.ts

@@ -31,6 +31,12 @@ test.describe("Pinned messages", () => {
         const tile = util.getEventTile("Msg1");
         await expect(tile).toMatchScreenshot("pinned-message-Msg1.png", {
             mask: [tile.locator(".mx_MessageTimestamp")],
+            css: `
+                // Hide the jump to bottom button in the timeline to avoid flakiness
+                .mx_JumpToBottomButton {
+                    display: none !important;
+                }
+            `,
         });
     });