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/mix/tasks/pleroma/database_test.exs

@@ -3,7 +3,7 @@
 # SPDX-License-Identifier: AGPL-3.0-only
 
 defmodule Mix.Tasks.Pleroma.DatabaseTest do
-  use Pleroma.DataCase
+  use Pleroma.DataCase, async: true
   use Oban.Testing, repo: Pleroma.Repo
 
   alias Pleroma.Activity