testdir: use existing monkeypatch fixture?

[blueyed]

Do you want this?
blueyed@b23b0df#diff-1284161c2c98c8aedd66545ff79a8af6R497

Needs to be decided for #6164.

[nicoddemus]

I'm fine with that change, except perhaps it should receive monkeypatch by argument (like done for request and tmpdir_factory) instead of using getfixturevalue.