tests: news: add test cases for previous news regressions

These tests would've caught the 3 previous regressions we had in the news feature
over the last year.

Verified by reverting each of the relevant fix commits (see below) and confirming
the relevant tests start to fail then pass again once the fix is cherry-picked in isolation.

See: 0e56f99
See: f1d98b6
See: 1ffaa70
Bug: https://bugs.gentoo.org/857669
Bug: https://bugs.gentoo.org/889330
Signed-off-by: Sam James <sam@gentoo.org>