CI: Run Linux AArch64 tests on real hardware

[tatsuya6502]

Currently, we are using QEMU's user mode emulation to run tests for Linux AArch64 target on x86_64 host, but it does not seem to emulate weak memory ordering in such an environment (crossbeam-rs/crossbeam#837).

Moka's lock-free concurrent hash table utilizes weak memory ordering whenever possible, so it would be better to run CI on real AArch64 hardware.

Cirrus CI provides Linux AArch64 containers.

[ClSlaid]

/assignme

[tatsuya6502]

@ClSlaid — Thank you for the offer. I have not done any further research on this. Maybe I have to create an account at Cirrus CI before get started? Please let me know if you need some assistance.

[ClSlaid]

Adding a Cirrus CI application to this repository is needed, and it's free of charge for public repositories, according to the CI's official documentation.