BUG/MINOR: h3: forbid 'Z' as well in header field names checks

BUG/MINOR: h3: forbid 'Z' as well in header field names checks

The current tests in _h3_handle_hdr() and h3_trailers_to_htx() check
for an interval between 'A' and 'Z' for letters in header field names
that should be forbidden, but mistakenly leave the 'Z' out of the
forbidden range, resulting in it being implicitly valid.

This has no real consequences but should be fixed for the sake of
protocol validity checking.

This must be backported to all relevant versions.

(cherry picked from commit ad75431b9c7eb739fa05f748098a9a505cf9c868)
Signed-off-by: Willy Tarreau <w@1wt.eu>
(cherry picked from commit 2c3eec71e195fa9b60b93e9b7532f55b827a22b3)
Signed-off-by: Willy Tarreau <w@1wt.eu>
(cherry picked from commit 65b8ac6c8681549e19643062897db3655b279ce4)
Signed-off-by: Willy Tarreau <w@1wt.eu>