fix failing test unit tests

requires to run validations for custom values every time, so we do it

there was no clear indication on why they should not run always, it was not apparent either

lib/plugins/acts_as_customizable/lib/acts_as_customizable.rb

@@ -47,7 +47,7 @@ module Redmine
                                    dependent: :delete_all,
                                    validate: false
           before_validation { |customized| customized.custom_field_values if customized.new_record? }
-          validate :validate_custom_values, if: -> (customized) { customized.custom_field_values_changed? }
+          validate :validate_custom_values
           send :include, Redmine::Acts::Customizable::InstanceMethods
           # Save custom values when saving the customized object
           after_save :save_custom_field_values

test/unit/time_entry_activity_test.rb

@@ -62,7 +62,8 @@ class TimeEntryActivityTest < ActiveSupport::TestCase
 
     e = TimeEntryActivity.new(name: 'Custom Data')
     assert !e.save
-    assert_include e.errors[:custom_values], I18n.translate('activerecord.errors.messages.invalid')
+    assert_include e.errors["custom_field_#{field.id}"],
+                   I18n.translate('activerecord.errors.messages.blank')
   end
 
   def test_create_with_required_custom_field_should_succeed
@@ -85,7 +86,7 @@ class TimeEntryActivityTest < ActiveSupport::TestCase
     # Blanking custom field, save should fail
     e.custom_field_values = { field.id => '' }
     assert !e.save
-    refute_empty e.errors[:custom_values]
+    refute_empty e.errors["custom_field_#{field.id}"]
 
     # Update custom field to valid value, save should succeed
     e.custom_field_values = { field.id => '0' }