models: require belong_to associations on commentaire

spec/factories/commentaire.rb

@@ -1,12 +1,8 @@
 FactoryBot.define do
   factory :commentaire do
-    body { 'plop' }
+    association :dossier, :en_construction
 
-    before(:create) do |commentaire, _evaluator|
-      if !commentaire.dossier
-        commentaire.dossier = create :dossier, :en_construction
-      end
-    end
+    body { 'plop' }
 
     trait :with_file do
       piece_jointe { Rack::Test::UploadedFile.new('spec/fixtures/files/logo_test_procedure.png', 'image/png') }