test(react-native): import vitest globals in TypingIndicator testid test

Matches the explicit-import convention used by sibling tests in this
package (e.g. copilot-chat-agentid.test.tsx, streaming-fetch.test.ts).
Removes 3 tsc "Cannot find name 'describe'/'it'/'expect'" errors
without changing runtime behavior — vitest globals already provided
at runtime via vitest.config.mjs (globals: true).

Author: jpr5

packages/react-native/src/components/messages/__tests__/TypingIndicator.testid.test.ts

@@ -1,3 +1,4 @@
+import { describe, it, expect } from "vitest";
 import { readFileSync } from "fs";
 import { resolve } from "path";