Do not trigger autopkgtest on all arches

[Dimitri John Ledkov]

Do not trigger autopkgtest on all arches

Currently riscv64 only kernels trigger a lot of autopkgtests on every architecture for no apparent reason.

Currently dpkg-source generates Testsuite triggers in .dsc, and all the britney machinery figures out that src:linux-riscv publishes at least one binary on a given architecture, and triggers tests.

This is because Package: SRCPKGNAME-headers-PKGVER-ABINUM is Architecture: all instead of Architecture: riscv64.

It is not easy to remove Testsuite-Triggers from the .dsc, however it is relatively harmless to switch riscv64 kernel header packages to be architecture riscv64. Afterall, they typically never build kernels for any other architectures and have no need to share headers package between architectures.

This should speed up riscv64 kernel migration through autopkgtest infrastructure without requesting a bunch of tests being done on a lot of architecutres ie. test systemd on all arches with trigger src:linux-riscv.