ci: test on armhf and arm64

This MR adds build+unit/config test coverage on 32b and 64b ARM.

The runners are Debian 10 LXC containers running on Turris Omnia (armhf) and Turris Mox (arm64).

Consider these two tests experimental and feel free to temporarily disable/ignore them in case something happens with the runners. Also, I've seen a few weird errors with config.doh2 on arm64, although I didn't reliably reproduce them - I'm not sure if those are real issues or not.

daemon/lua/meson.build

@@ -5,7 +5,7 @@ config_tests += [
   ['controlsock', files('controlsock.test.lua')],
   ['krprint', files('krprint.test.lua')],
   ['ta', files('trust_anchors.test/ta.test.lua')],
-  ['ta_bootstrap', files('trust_anchors.test/bootstrap.test.lua')],
+  ['ta_bootstrap', files('trust_anchors.test/bootstrap.test.lua'), ['y2k38']],
 ]
 
 integr_tests += [