rails: fix deprecated #to_s(:format) method.

Fix this deprecation:

    Deprecate passing a format to #to_s in favor of #to_formatted_s in
    Array, Range, Date, DateTime, Time, BigDecimal, Float and, Integer.

https://guides.rubyonrails.org/7_0_release_notes.html#active-support-deprecations

app/logical/discord_slash_command/post_embed.rb

@@ -52,7 +52,7 @@ class DiscordSlashCommand
 
     def embed_footer
       dimensions = "#{post.image_width}x#{post.image_height}"
-      file_size = post.file_size.to_s(:human_size, precision: 4)
+      file_size = post.file_size.to_formatted_s(:human_size, precision: 4)
       text = "#{post.fav_count} ❤ | Rating: #{post.rating.upcase} | #{dimensions} (#{file_size} #{post.file_ext})"
 
       { text: text }