refa(tests): enable async true in client report sender test

Author: solnic

test/sentry/client_report/sender_test.exs

@@ -1,5 +1,5 @@
 defmodule Sentry.ClientReportTest do
-  use Sentry.Case, async: false
+  use Sentry.Case, async: true
 
   import Sentry.TestHelpers