Preload user attachments before creating avatar_url list.

To avoid n+1 attachment queries.
Problem exists on `documents/new` and `documents/:id/edit` when document category is Experimental
and BlockNoteJS editor is enabled.

Author: ba1ash

lib/primer/open_project/forms/block_note_editor.rb

@@ -51,7 +51,7 @@ def initialize(input:, value:, document_id:)
           super()
           @input = input
           @value = value
-          @users = User.active.map do |user|
+          @users = User.active.preload(:attachments).map do |user|
             {
               id: user.id,
               username: user.name,