[3.12] gh-111942: Fix SystemError in the TextIOWrapper constructor (GH-112061) (GH...

[3.12] gh-111942: Fix SystemError in the TextIOWrapper constructor (GH-112061) (GH-112089)

In non-debug more the check for the "errors" argument is skipped,
and then PyUnicode_AsUTF8() can fail, but its result was not checked.

Co-authored-by: Victor Stinner <vstinner@python.org>
(cherry picked from commit 9302f05f9af07332c414b3c19003efd1b1763cf3)

Co-authored-by: Serhiy Storchaka <storchaka@gmail.com>