FIX: correctly show validation errors in automation (#27622)

A previous refactor has prevented errors to show correctly. The guilt of the issue is that we were not calling the error variable correctly in the templates.

This commit also adds a spec for this case, and removes the need for `I18n.backend.store_translations` in specs so we don't have to write too much boilerplate each time we write a spec.

plugins/automation/spec/system/error_spec.rb

@@ -0,0 +1,34 @@
+# frozen_string_literal: true
+
+describe "DiscourseAutomation | error", type: :system do
+  fab!(:admin)
+
+  before do
+    SiteSetting.discourse_automation_enabled = true
+    sign_in(admin)
+  end
+
+  context "when saving the form with an error" do
+    it "shows the error correctly" do
+      visit("/admin/plugins/discourse-automation")
+
+      find(".new-automation").click
+      fill_in("automation-name", with: "aaaaa")
+      select_kit = PageObjects::Components::SelectKit.new(".scriptables")
+      select_kit.expand
+      select_kit.select_row_by_value("post")
+      find(".create-automation").click
+      select_kit = PageObjects::Components::SelectKit.new(".triggerables")
+      select_kit.expand
+      select_kit.select_row_by_value("recurring")
+      find(".update-automation").click
+
+      expect(page).to have_content(
+        I18n.t(
+          "discourse_automation.models.fields.required_field",
+          { name: "topic", target: "script", target_name: "post" },
+        ),
+      )
+    end
+  end
+end