Make db-dependent tests sync

As explained at
https://hexdocs.pm/ecto_sqlite3/Ecto.Adapters.SQLite3.html#module-async-sandbox-testing:

The Ecto SQLite3 adapter does not support async tests when used with
Ecto.Adapters.SQL.Sandbox. This is due to SQLite only allowing up one
write transaction at a time, which often does not work with the Sandbox
approach of wrapping each test in a transaction.

test/music_library_web/controllers/cover_controller_test.exs

@@ -1,5 +1,5 @@
 defmodule MusicLibraryWeb.CoverControllerTest do
-  use MusicLibraryWeb.ConnCase, async: true
+  use MusicLibraryWeb.ConnCase
 
   import MusicLibrary.RecordsFixtures
 

test/music_library_web/controllers/stats_controller_test.exs

@@ -1,5 +1,5 @@
 defmodule MusicLibraryWeb.StatsControllerTest do
-  use MusicLibraryWeb.ConnCase, async: true
+  use MusicLibraryWeb.ConnCase
 
   alias MusicLibrary.Records.Record
 

test/music_library_web/live/record_index_test.exs

@@ -1,5 +1,5 @@
 defmodule MusicLibraryWeb.RecordIndexTest do
-  use MusicLibraryWeb.ConnCase, async: true
+  use MusicLibraryWeb.ConnCase
 
   import Phoenix.LiveViewTest
   import MusicLibrary.RecordsFixtures

test/music_library_web/live/record_show_test.exs

@@ -1,5 +1,5 @@
 defmodule MusicLibraryWeb.RecordShowTest do
-  use MusicLibraryWeb.ConnCase, async: true
+  use MusicLibraryWeb.ConnCase
 
   import Phoenix.LiveViewTest
   import MusicLibrary.RecordsFixtures