Tests: Make as many tests as possible async.

In general, tests that match these criteria can be made async:

- Doesn't use real Cachex.
- Doesn't write to the Config / Application Environment.
- Uses Mock. Using Mox is fine.
- Uses the streamer.

test/pleroma/activity/ir/topics_test.exs

@@ -3,7 +3,7 @@
 # SPDX-License-Identifier: AGPL-3.0-only
 
 defmodule Pleroma.Activity.Ir.TopicsTest do
-  use Pleroma.DataCase
+  use Pleroma.DataCase, async: true
 
   alias Pleroma.Activity
   alias Pleroma.Activity.Ir.Topics

test/pleroma/activity/search_test.exs

@@ -7,7 +7,7 @@ defmodule Pleroma.Activity.SearchTest do
   alias Pleroma.Web.CommonAPI
   import Pleroma.Factory
 
-  use Pleroma.DataCase
+  use Pleroma.DataCase, async: true
 
   test "it finds something" do
     user = insert(:user)