Simplify touching a budget when a phase changes

The `belongs_to` method already has that option, so there's no need to
do it manually in an `after_save` callback.

app/models/budget/phase.rb

@@ -11,7 +11,7 @@ class Budget
     include Globalizable
     include Sanitizable
 
-    belongs_to :budget
+    belongs_to :budget, touch: true
     belongs_to :next_phase, class_name: self.name, inverse_of: :prev_phase
     has_one :prev_phase, class_name: self.name, foreign_key: :next_phase_id, inverse_of: :next_phase
 
@@ -24,7 +24,6 @@ class Budget
     validate :next_phase_dates_valid?
 
     after_save :adjust_date_ranges
-    after_save :touch_budget
 
     scope :enabled,           -> { where(enabled: true) }
     scope :published,         -> { enabled.where.not(kind: "drafting") }
@@ -70,10 +69,6 @@ class Budget
         end
       end
 
-      def touch_budget
-        budget.touch
-      end
-
       def prev_phase_dates_valid?
         if enabled? && starts_at.present? && prev_enabled_phase.present?
           prev_enabled_phase.assign_attributes(ends_at: starts_at)

spec/models/budget/phase_spec.rb

@@ -115,6 +115,18 @@ describe Budget::Phase do
     end
   end
 
+  describe "#save" do
+    it "touches the budget when it's updated" do
+      budget = create(:budget)
+
+      travel(10.seconds) do
+        budget.current_phase.update!(enabled: false)
+
+        expect(budget.updated_at).to eq Time.current
+      end
+    end
+  end
+
   describe "#adjust_date_ranges" do
     let(:prev_enabled_phase) { second_phase.prev_enabled_phase }
     let(:next_enabled_phase) { second_phase.next_enabled_phase }