fix: assign_to.procedure_presentation should return an ActiveModel::Errors if needed

the caller will then calls `errors.full_messages`

app/models/assign_to.rb

@@ -24,7 +24,9 @@ class AssignTo < ApplicationRecord
     errors = begin
                procedure_presentation.errors if procedure_presentation&.invalid?
              rescue ActiveRecord::RecordNotFound => e
-               [e.message]
+               errors = ActiveModel::Errors.new(self)
+               errors.add(:procedure_presentation, e.message)
+               errors
              end
 
     if errors.present?

spec/models/assign_to_spec.rb

@@ -45,7 +45,7 @@ describe AssignTo, type: :model do
       it do
         expect(procedure_presentation_or_default).to be_persisted
         expect(procedure_presentation_or_default).to be_valid
-        expect(errors).to be_present
+        expect(errors.full_messages).to include(/unable to find procedure 666/)
         expect(assign_to.procedure_presentation).not_to be(procedure_presentation)
       end
     end