bpo-41818: Close file descriptors in test_openpty

[encukou]

When stdin is a TTY, the test added in commit c13d899
is expected to fail. However, when it failed, it did not close
its file descriptors. This is flagged by the refleak tests (but
only when stdin is a TTY, which doesn't seem to be the case on CI).

https://bugs.python.org/issue41818

[8vasu]

@encukou can you please check my request in the python issue?

[encukou]

The comment there was:

That test was created by modifying an existing test which already had that issue; it is documented in a comment by user nnorwitz in the file. If your solution resolves the problem for all the tests in "class PtyTest", then can you please also remove that comment?

I'm not that concerned about failing tests leaking – leak checks are run with the tests, so if tests fail, leaking doesn't really matter.
But test_openpty is sometimes expected to fail, and in that case, the test suite succeeded but leaked.

Anyway, I've modified the other tests and removed the comment.

[bedevere-bot]

🤖 New build scheduled with the buildbot fleet by @zware for commit 494fd7b 🤖

If you want to schedule another build, you need to add the ":hammer: test-with-buildbots" label again.

[encukou]

There's a failure in test_curses, test timeout in test_asyncio, and ... a BuildBot error, it seems.
bpo-41701 makes these issues quite hard to investigate, but it looks like they're not related to this PR.