t9350: fix encoding test to actually test reencoding

t9350: fix encoding test to actually test reencoding

This test used an author with non-ascii characters in the name, but no
special commit message.  It then grep'ed for those non-ascii characters,
but those are guaranteed to exist regardless of the reencoding process
since the reencoding only affects the commit message, not the author or
committer names.  As such, the test would work even if the re-encoding
process simply stripped the commit message entirely.  Modify the test to
actually check that the reencoding into UTF-8 worked.

Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>