CI: Support armv7 as host platform

(Re)enable armv7 as a host platform in CI.

As of writing, the sole armv7 job in the MR pipeline does not run by default, is allowed to fail, and has failed for 95% of jobs in the previous month. Furthermore, we are about to shut down the only runners that supported the architecture. (#22289 (closed))

This ticket tracks our eventual continuation of armv7 support.