FIX: instantly removes group message when leaving (#25961)

Prior to this fix clicking <kbd>x</kdb> on a channel row would effectively leave the channel on server side, but it wouldn't disappear from the screen before a page refresh.

plugins/chat/spec/system/drawer/index_spec.rb

@@ -0,0 +1,43 @@
+# frozen_string_literal: true
+
+RSpec.describe "Drawer - index", type: :system do
+  fab!(:current_user) { Fabricate(:user) }
+
+  let(:drawer_page) { PageObjects::Pages::ChatDrawer.new }
+
+  before do
+    chat_system_bootstrap
+    sign_in(current_user)
+  end
+
+  it "can leave a direct message" do
+    channel = Fabricate(:direct_message_channel, users: [current_user])
+    row = PageObjects::Components::Chat::ChannelRow.new(channel.id)
+
+    drawer_page.visit_index
+
+    expect(row).to exist
+
+    row.leave
+
+    expect(row).to be_non_existent
+  end
+
+  it "can leave a group message" do
+    channel =
+      Fabricate(
+        :direct_message_channel,
+        group: true,
+        users: [current_user, Fabricate(:user), Fabricate(:user)],
+      )
+    row = PageObjects::Components::Chat::ChannelRow.new(channel.id)
+
+    drawer_page.visit_index
+
+    expect(row).to exist
+
+    row.leave
+
+    expect(row).to be_non_existent
+  end
+end