rabbitmq_cli: Fix invalid feature flag definitions

`desc` was set to binaries instead of strings.

Author: dumbbell

deps/rabbitmq_cli/test/ctl/enable_feature_flag_test.exs

@@ -19,7 +19,7 @@ defmodule EnableFeatureFlagCommandTest do
 
     new_feature_flags = %{
       @feature_flag => %{
-        desc: "My feature flag",
+        desc: 'My feature flag',
         provided_by: :EnableFeatureFlagCommandTest,
         stability: :stable
       }

deps/rabbitmq_cli/test/ctl/list_feature_flags_command_test.exs

@@ -21,12 +21,12 @@ defmodule ListFeatureFlagsCommandTest do
 
     new_feature_flags = %{
       @flag1 => %{
-        desc: "My feature flag #1",
+        desc: 'My feature flag #1',
         provided_by: :ListFeatureFlagsCommandTest,
         stability: :stable
       },
       @flag2 => %{
-        desc: "My feature flag #2",
+        desc: 'My feature flag #2',
         provided_by: :ListFeatureFlagsCommandTest,
         stability: :stable
       }