scheduler: Trigger for packages listing us in Testsuite-Triggers

When building a source package, for all packages with autopkgtests, dpkg-source will create a Testsuite-Triggers field. This field is exported in the Sources indices for APT. Quoting dsc(5).

Testsuite-Triggers: package-list

This field declares the comma-separated union of all test dependencies (Depends fields in debian/tests/control file), with all restrictions removed, and OR dependencies flattened (that is, converted to separate AND relationships), except for binaries generated by this source package and its meta-dependency equivalent @.

It's possible for d/tests/control Depends to include us even if d/control Depends doesn't. autopkgtests can be arbitrarily elaborate, somebody could be using us to benchmark some other library, for example.

We wouldn't discover this now, for lack of a reverse dependency relation. But we know that being listed in Testsuite-Triggers of a package must affect that package's autopkgtests, so we definitely need to schedule tests for any packages that list our ROCm packages there.