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

[romuald]

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-144433: clarify patch.dict behavior #144434