runes: fix test breakage

Missed these tests when fixing try handling. (\xc0 is now always
treated as illegal UTF-8 and not considered as a short sequence.)

TBR

Change-Id: Iff7047c506e9a740a698bb1ac85537bb439f441b
Reviewed-on: https://go-review.googlesource.com/17706
Reviewed-by: Marcel van Lohuizen <mpvl@golang.org>
1 file changed