Lintian tasks generally fail for stretch ELTS

This effectively is a support ticket from Freexian.

Our lintian workrequests tend to generally fail. A recent example is https://debusine.freexian.com/freexian/elts/work-request/8421/. You do not see a suitable error message there due to #589 (closed). What really happens is that Debusine found an arm64 to be available and directed the lintian task there. Then it tried to look up a suitable chroot from the freexian collection. It figured that there is no arm64 chroot as stretch is only available for amd64, armhf and i386. Then, it gave up.

The resulting behavior is less than ideal. It may be argued that the choice of worker architecture is less than ideal, but it may also be argued that the workflow as improperly configured failing to restrict that choice of worker architecture. If the latter is the case, I request assistance with updating the workflow template.