Prevent history visible banner from displaying in threads. (#31535)

* fix: Prevent history visible banner from displaying in threads.

* tests: Verify banner is not visible in threads.

test/unit-tests/components/viewmodels/composer/HistoryVisibleBannerViewModel-test.tsx

@@ -104,6 +104,29 @@ describe("HistoryVisibleBannerViewModel", () => {
         vm.dispose();
     });
 
+    it("should not show the banner in threads", () => {
+        upsertRoomStateEvents(room, [
+            mkEvent({
+                event: true,
+                type: "m.room.encryption",
+                user: "@user1:server",
+                content: {},
+            }),
+            mkEvent({
+                event: true,
+                type: "m.room.history_visibility",
+                user: "@user1:server",
+                content: {
+                    history_visibility: "shared",
+                },
+            }),
+        ]);
+
+        const vm = new HistoryVisibleBannerViewModel({ room, threadId: "some thread ID" });
+        expect(vm.getSnapshot().visible).toBe(false);
+        vm.dispose();
+    });
+
     it("should show the banner in encrypted rooms with non-joined history visibility", async () => {
         upsertRoomStateEvents(room, [
             mkEvent({