When checking if days are the current or the next day, we did not take the
local timezone into account. Therefore, if the local timezone was not
UTC, the previous or next day could erroneously be detected as `today`
(same error for `tomorrow`).

The default (today) was until now not localized, but today in UTC was
assumed. This could lead to commands such as `khal calendar` starting
to show events from with either the previous or the next day instead of
today.

for more information, see https://pre-commit.ci