[7.1.x] docs(monkeypatch): Fix autodoc reference links

[github-actions]

Backport of PR #10013 to 7.1.x branch. PR created by backport workflow.

[tony]

@nicoddemus We may want this backported to 7.0.x and 6.2.x

works: https://docs.pytest.org/en/4.6.x/monkeypatch.html
breaks: https://docs.pytest.org/en/7.0.x/how-to/monkeypatch.html, https://docs.pytest.org/en/6.2.x/monkeypatch.html

should i make PRs for those?

[nicoddemus]

@tony thanks, created #10016 for 7.0.x, could you open a PR for 6.2.x then?

[tony]

@nicoddemus Yes. Making a 6.2.x one now

[tony]

@nicoddemus 6.2.x backport #10017