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

从 warnings 文档开始，查看所链接的 pytest 讨论中的示例，并将提供的函数与 -W 和 PYTHONWARNINGS 进行比较。完成的标准是文档包含匹配不同 warning 类型的示例，并清楚说明这些方法在哪些方面表现不同。