test: new: Fix intermittent test failures with --debug

test: new: Fix intermittent test failures with --debug

Although messages are created in a particular order, it seems that
when they are created on a tmpfs, they do not always come back in the
same order, leading to the same files being ignored but being output
in a different order. This causes the test to fail because the outputs
being compared are the same.

Fix the failures by sorting the output of notmuch --debug and
comparing this to a hand-sorted version of its output.

Signed-off-by: Ethan Glasser-Camp <ethan@betacantrips.com>