testset: Use a slightly larger size for "largefile"

testset/binary seems to have suddenly stopped emitting
arch-dep-package-has-big-usr-share.  Increasing the size of
"largefile" restores the tag, so presumably the test was just a bit
too close to the cut-off edge.

Signed-off-by: Niels Thykier <niels@thykier.net>