test(addons): expect the stale banner in the apps polling spec

The list stays on screen with a banner when a refresh fails. The banner
text changed from "may be out of date" to "Showing the last known
state.", so the polling spec waited for text that is no longer shown.
Assert the banner by its test id, as the busy-owner spec does.

Assisted-by: Claude:claude-sonnet-5-5

core/http/react-ui/e2e/addons-gallery.spec.js

@@ -243,14 +243,14 @@ test.describe('Add-ons: apps', () => {
     await page.clock.runFor(200)
     await expect.poll(() => state.log.appsList).toBe(2)
     // The failure doubles the wait, and the old list stays visible and flagged.
-    await expect(page.getByText('may be out of date')).toBeVisible()
+    await expect(page.getByTestId('addons-stale')).toBeVisible()
     await page.clock.runFor(9_000)
     expect(state.log.appsList).toBe(2)
     await page.clock.runFor(1_500)
     await expect.poll(() => state.log.appsList).toBe(3)
     await page.clock.runFor(21_000)
     await expect.poll(() => state.log.appsList).toBe(4)
-    await expect(page.getByText('may be out of date')).toHaveCount(0)
+    await expect(page.getByTestId('addons-stale')).toHaveCount(0)
     // Leave for a route without a mounted add-on consumer (Home keeps commands current).
     await page.evaluate(() => { window.history.pushState({}, '', '/app/polling-left'); window.dispatchEvent(new PopStateEvent('popstate')) })
     // The route loads lazily and the page clock is paused: let the transition