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/emoji/formatter_test.exs

@@ -4,7 +4,7 @@
 
 defmodule Pleroma.Emoji.FormatterTest do
   alias Pleroma.Emoji.Formatter
-  use Pleroma.DataCase
+  use Pleroma.DataCase, async: true
 
   describe "emojify" do
     test "it adds cool emoji" do

test/pleroma/emoji/pack_test.exs

@@ -3,7 +3,7 @@
 # SPDX-License-Identifier: AGPL-3.0-only
 
 defmodule Pleroma.Emoji.PackTest do
-  use ExUnit.Case, async: true
+  use Pleroma.DataCase
   alias Pleroma.Emoji.Pack
 
   @emoji_path Path.join(