tests: ensure we don't see database errors during duplicate insert

tests: ensure we don't see database errors during duplicate insert

Currently, the parser causes IntegrityErrors while inserting duplicate
patches; these tend to pollute database logs.

This change adds a check, which currently fails, to ensure we do not
cause errors during a duplicate patch parse.

Signed-off-by: Jeremy Kerr <jk@ozlabs.org>
Signed-off-by: Stephen Finucane <stephen@that.guru>
[stephenfin: Add 'expectedFailure' marker to keep all tests green]