tools: Don't run slow unit tests on RISC-V architectures in Debian/Ubuntu
tools: Don't run slow unit tests on RISC-V architectures in Debian/Ubuntu

Currently all available buildds are emulated, and thus very slow. It
takes way more than 10 minutes to run test-tls-certfile, so skip that
and other slow unit tests on this architecture.

Closes #14216
deryni/cockpit,deryni/cockpit,garrett/cockpit,moraleslazaro/cockpit,mvollmer/cockpit,moraleslazaro/cockpit,mvollmer/cockpit,cockpit-project/cockpit,deryni/cockpit,deryni/cockpit,mvollmer/cockpit,moraleslazaro/cockpit,cockpit-project/cockpit,moraleslazaro/cockpit,moraleslazaro/cockpit,martinpitt/cockpit,cockpit-project/cockpit,mvollmer/cockpit,martinpitt/cockpit,martinpitt/cockpit,garrett/cockpit,deryni/cockpit,deryni/cockpit,cockpit-project/cockpit,garrett/cockpit,martinpitt/cockpit,moraleslazaro/cockpit,garrett/cockpit,moraleslazaro/cockpit,cockpit-project/cockpit,mvollmer/cockpit,garrett/cockpit,deryni/cockpit,martinpitt/cockpit