FIX: ensures global notices are destroyed on post created (#28684)

Prior to this fix we could exit early if tags was `[]` as `tags && (tags & post.topic.tags.map(&:name)).empty?` would have returned true. This commit ensures it's not the case anymore and adds a test for it.

Co-Authored-By: Martin Brennan <mjrbrennan@gmail.com>

plugins/automation/spec/lib/discourse_automation/event_handlers_spec.rb

@@ -0,0 +1,24 @@
+# frozen_string_literal: true
+
+describe DiscourseAutomation::EventHandlers do
+  describe "#handle_stalled_topic" do
+    context "when tags are empty" do
+      fab!(:automation) do
+        Fabricate(:automation, trigger: DiscourseAutomation::Triggers::STALLED_TOPIC, enabled: true)
+      end
+      fab!(:user)
+      fab!(:post) { Fabricate(:post, user: user) }
+
+      before do
+        automation.upsert_field!("tags", "tags", { value: [] }, target: "trigger")
+        Fabricate(:user_global_notice, identifier: automation.id, user_id: user.id)
+      end
+
+      it "destroys notices" do
+        expect { DiscourseAutomation::EventHandlers.handle_stalled_topic(post) }.to change {
+          DiscourseAutomation::UserGlobalNotice.count
+        }.by(-1)
+      end
+    end
+  end
+end