Add more examples in the `warnings` docs

This is a follow-up of GH-86438 and GH-23172. The warnings docs should include more examples to show how to match different types of warnings using both the provided functions and -W/PYTHONWARNINGS, especially since they behave differently.

At the bottom of https://github.com/pytest-dev/pytest/discussions/8759#discussioncomment-2818984 there are already some examples to illustrate some of the differences, even though some are specific to pytest.

Linked PRs

• gh-106618

從 warnings 文件開始，查看所連結的 pytest 討論中的範例，並將提供的函式與 -W 和 PYTHONWARNINGS 進行比較。完成的標準是文件包含比對不同 warning 類型的範例，並清楚說明這些方法在哪些方面表現不同。