[3.11] gh-94823: Improve coverage in tokenizer.c:valid_utf8 (GH-94856) by miss-islington · Pull Request #96029 · python/cpython

…94856)

When loading a source file from disk, there is a separate UTF-8 validator
distinct from the one in `unicode_decode_utf8`. This exercises that code path
with the same set of invalid inputs as we use for testing the "other" UTF-8
decoder.
(cherry picked from commit f215d7c)

Co-authored-by: Michael Droettboom <mdboom@gmail.com>