Force local apt release repos to be trusted

Building a binary that depends on locally-created debs from a previous Jenkins build that are bind mounted into `/tmp/apt-$$` fails if they are untrusted. Since it is assumed that what we force into `/tmp/apt-$$`, say for a release build, is (almost by definition) trusted, I've added `[trusted=yes]` to the deb sources as described in https://wiki.debian.org/PbuilderTricks#How_to_include_local_packages_in_the_build.