FIX: resets pending automations only if necessary (#26685)

Prior to this fix, any change to an automation would reset `pending_automations`, now we only do it if any value related to recurrence (start_date, interval, frequency, execute_at...) has been changed.

It means that any trigger creating `pending_automations` now needs to manage them in the `on_update` callback.

plugins/automation/spec/triggers/point_in_time_spec.rb

@@ -40,4 +40,49 @@ describe "PointInTime" do
       end
     end
   end
+
+  context "when updating automation" do
+    fab!(:automation) do
+      Fabricate(:automation, trigger: DiscourseAutomation::Triggers::POINT_IN_TIME, script: "test")
+    end
+
+    before do
+      DiscourseAutomation::Scriptable.add("test") do
+        triggerables [DiscourseAutomation::Triggers::POINT_IN_TIME]
+        field :test, component: :text
+      end
+
+      automation.upsert_field!(
+        "execute_at",
+        "date_time",
+        { value: 2.hours.from_now },
+        target: "trigger",
+      )
+
+      automation.upsert_field!("test", "text", { value: "something" }, target: "script")
+    end
+
+    context "when execute_at changes" do
+      it "resets the pending automations" do
+        expect {
+          automation.upsert_field!(
+            "execute_at",
+            "date_time",
+            { value: 3.hours.from_now },
+            target: "trigger",
+          )
+        }.to change { DiscourseAutomation::PendingAutomation.last.execute_at }
+        expect(DiscourseAutomation::PendingAutomation.count).to eq(1)
+      end
+    end
+
+    context "when a field other than execute_at changes" do
+      it "doesn't reset the pending automations" do
+        expect {
+          automation.upsert_field!("test", "text", { value: "somethingelse" }, target: "script")
+        }.to_not change { DiscourseAutomation::PendingAutomation.last.execute_at }
+        expect(DiscourseAutomation::PendingAutomation.count).to eq(1)
+      end
+    end
+  end
 end