t0050: mark non-working test as such

t0050: mark non-working test as such

The test is to prepare an empty file "camelcase" in the index, remove
and replace it with another file "CamelCase" with "1" as its contents
in the working tree, and add it to the index, in a repository configured
to be case insensitive.

However, the test actually checked ls-files knows about a pathname that
matches "camelcase" case insensitively.  It didn't check if the added
contents actually was the updated one.

Mark the test as non-working.

Signed-off-by: Junio C Hamano <gitster@pobox.com>