TST: Add test for CoW in pop

[phofl]

• xref ENH / CoW: Use the "lazy copy" (with Copy-on-Write) optimization in more methods where appropriate #49473 (Replace xxxx with the GitHub issue number)
• Tests added and passed if fixing a bug or adding a new feature
• All code checks passed.
• Added type annotations to new arguments/methods/functions.
• Added an entry in the latest doc/source/whatsnew/vX.X.X.rst file if fixing a bug or adding a new feature.

cc @jorisvandenbossche
No change in behavior but confirming the behavior

[jorisvandenbossche]

Looks good!

[jorisvandenbossche]

Suggested change

	assert not np.shares_memory(result.values, get_array(view_original, "a"))
	assert not np.shares_memory(result.values, get_array(view_original, "a"))
	assert df.iloc[0, 0] == 1

To ensure the original wasn't modified?

[jorisvandenbossche]

Ah, no, nevermind. pop of course removed that column from df, so we don't have to check it there, and that's the wholeponit of having this view_original (which is already checked below that it is still equal to the original dataframe)

[jorisvandenbossche]

Failures are unrelated sqlalchemy failures