Fix public posts from silenced accounts not being changed to unlisted visibility (#13096)

app/services/post_status_service.rb

@@ -50,7 +50,7 @@ class PostStatusService < BaseService
   def preprocess_attributes!
     @text         = @options.delete(:spoiler_text) if @text.blank? && @options[:spoiler_text].present?
     @visibility   = @options[:visibility] || @account.user&.setting_default_privacy
-    @visibility   = :unlisted if @visibility == :public && @account.silenced?
+    @visibility   = :unlisted if @visibility&.to_sym == :public && @account.silenced?
     @scheduled_at = @options[:scheduled_at]&.to_datetime
     @scheduled_at = nil if scheduled_in_the_past?
   rescue ArgumentError