Re-add two lintian overrides about (well known) source-is-missing

It's just that with those two locally I get mismatched override warning
(which is wrong), while without then the jenkins jobs throws a lintian error.

So erring on the side of caution not to cause an error, but rather a warning.

Signed-off-by: Holger Levsen <holger@layer-acht.org>