Copy-on-Write Guide - "Previous behavior" output is what would happen post-migration to CoW

[gah-bo]

Pandas version checks

• I have checked that the issue still exists on the latest versions of the docs on main here

Location of the documentation

https://pandas.pydata.org/docs/dev/user_guide/copy_on_write.html

Documentation problem

Copy-on-Write (CoW) section of "Previous behavior" states that the behavior before CoW leads to this output:

In [1]: df = pd.DataFrame({"foo": [1, 2, 3], "bar": [4, 5, 6]})

In [2]: subset = df["foo"]

In [3]: subset.iloc[0] = 100

In [4]: df
Out[4]: 
   foo  bar
0    1    4
1    2    5
2    3    6

But that's the behavior that would happen after migrating to CoW

Note: this codeblock seems to be used more than once, each time having this issue

Suggested fix for documentation

Actually show "Previous behavior" on the codeblock

[rhshadrach]

cc @phofl