mobile ci: exercise arm64 emulator as part of Android ci checks

We've recently hit an issue (fixed in https://github.com/envoyproxy/envoy/pull/24947) that surfaced only when launching the app on arm64 emulator (as opposed to x86 which are currently used by us). It may be worth modifying our Android CI jobs so that at least one of them uses arm64 emulator as opposed to x86 one.