[docs] Specify that unittest.mock.patch.dict does not make a deepcopy

Documentation

I always assumed that unittest.mock.patch.dict made a recursive (deep) copy of the dict and restored it afterwards.
It turns out it is a "simple" copy()

We should maybe clarify that in the documentation

Example:

foo = {
  "bar": {"baz": 1}
}

with patch.dict(foo, {"unrelated": 123}):
  foo["bar"]["baz"] = 2

# baz will stay at 2, assumed it was reset to the original 1

Linked PRs

• gh-144434

从 unittest.mock.patch.dict 文档开始，检查现有的关于如何恢复字典的说明。明确说明它使用的是浅拷贝，而不是递归 deepcopy，并使用 issue 中的嵌套字典示例来展示内部更改仍会保留。编辑后检查文档构建。