Only log subscription history when applicable

Previously we would create a GitlabSubscriptionHistory record whenever a
GitlabSubscription was updated, regardless of what changed. Now we will
only create that record if a tracked attribute has been updated.

ee/app/models/gitlab_subscription.rb

@@ -12,7 +12,7 @@ class GitlabSubscription < ApplicationRecord
   attribute :start_date, default: -> { Date.today }
 
   before_update :set_max_seats_used_changed_at
-  before_update :log_previous_state_for_update
+  before_update :log_previous_state_for_update, if: :tracked_attributes_changed?
   before_update :reset_seat_statistics
   before_update :publish_subscription_renewed_event
 
@@ -200,4 +200,8 @@ def new_term?
   def reset_seat_statistics?
     new_term? || (max_seats_used_changed_at.present? && max_seats_used_changed_at.to_date < start_date)
   end
+
+  def tracked_attributes_changed?
+    changed.intersection(GitlabSubscriptionHistory::TRACKED_ATTRIBUTES).any?
+  end
 end

ee/spec/models/gitlab_subscription_spec.rb

@@ -596,16 +596,26 @@
         )
       end
 
-      it 'logs previous state to gitlab subscription history' do
-        gitlab_subscription.update!(max_seats_used: 32)
+      context 'when a tracked attribute is updated' do
+        it 'logs previous state to gitlab subscription history' do
+          gitlab_subscription.update!(max_seats_used: 32)
+
+          expect(GitlabSubscriptionHistory.count).to eq(1)
+          expect(GitlabSubscriptionHistory.last.attributes).to include(
+            'gitlab_subscription_id' => gitlab_subscription.id,
+            'change_type' => 'gitlab_subscription_updated',
+            'max_seats_used' => 42,
+            'seats' => 13
+          )
+        end
+      end
 
-        expect(GitlabSubscriptionHistory.count).to eq(1)
-        expect(GitlabSubscriptionHistory.last.attributes).to include(
-          'gitlab_subscription_id' => gitlab_subscription.id,
-          'change_type' => 'gitlab_subscription_updated',
-          'max_seats_used' => 42,
-          'seats' => 13
-        )
+      context 'when tracked attributes are not updated' do
+        it 'does not log previous state to gitlab subscription history' do
+          expect do
+            gitlab_subscription.update!(last_seat_refresh_at: Time.current)
+          end.to not_change(GitlabSubscriptionHistory, :count)
+        end
       end
 
       context 'when max_seats_used has changed' do