style: rubocop fixes

.rubocop.yml

@@ -3,6 +3,8 @@ inherit_gem:
 
 Style/ClassVars:
   Enabled: false
+Style/ConditionalAssignment:
+  Enabled: false
 Style/GlobalVars:
   Enabled: false
 Style/FrozenStringLiteralComment:

lib/nexus_semantic_logger/appender_filter.rb

@@ -70,8 +70,6 @@ module NexusSemanticLogger
       @@names_fatal = nil
     end
 
-    private
-
     def self.fetch_env_names(var)
       ENV.fetch(var, '').split(',').to_set
     end