Rewrite integration test for forgot-password-test component

# Problem

Currently, `tests/integration/components/password/forgot-password-test.js` doesn't make full use of its page object by not defining a renderPage() function. To dry up the code, you can set a renderPage() function above the moduleForComponent, pass in the needed hbs selectors, and call renderPage() in each test.

References
#1605

從 tests/integration/components/password/forgot-password-test.js 開始，檢查其 page object 目前的使用方式。在 moduleForComponent 上方使用所需的 hbs 選擇器定義 renderPage()，然後在每個測試中呼叫它。當整合測試仍然通過且重複的設定已移除時，即表示完成。

由索引模型根據 Issue 內容生成。