t4067: make rename detection test output raw diff

t4067: make rename detection test output raw diff

95acf11a3d ("diff: restrict when prefetching occurs", 2020-04-07) taught
diff to prefetch blobs in a more limited set of situations. These
limited situations include when the output format requires blob data,
and when inexact rename detection is needed.

There is an existing test case that tests inexact rename detection, but
it also uses an output format that requires blob data, resulting in the
inexact-rename-detection-only code not being tested. Update this test to
use the raw output format, which does not require blob data.

Thanks to Derrick Stolee for noticing this lapse in code coverage and
for doing the preliminary analysis [1].

[1] https://lore.kernel.org/git/853759d3-97c3-241f-98e1-990883cd204e@gmail.com/

Signed-off-by: Jonathan Tan <jonathantanmy@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>