ci: Figure out how to setup arm64 and arm32 builds/tests

[Yawning]

While there are a number of build tags to try to force the no assembly and 32-bit backends to be build and exercised this really should build and test with an actual 32-bit toolchain/system so that stupid errors can be caught.

As we don't care about performance, QEMU or something should be sufficient here.

[Yawning]

CI will at least try building the module with 32-bit ARM, so hopefully this will catch some of the simple stupidity. We should still test on ARM to catch advanced stupidity though.

https://github.com/oasisprotocol/curve25519-voi/commit/e10f9a3a3cdc3db668ffdf04fc5c0166e4c3c223