ci: test on Android

[mxinden]

quinn-rs/quinn#1950 adds a GitHub job, testing quinn on Android.

Neqo doesn't have much platform specific code other than:

neqo/neqo-crypto/build.rs

Lines 226 to 229 in c80630b

	} else if env::consts::OS == "android" {
	builder = builder.clang_arg("-DLINUX");
	builder = builder.clang_arg("-DANDROID");
	}

That said, Neqo's dependencies have platform dependent code and Android is a tier 1 Firefox build target.

Objections to adding the same CI job to Neqo?

[larseggert]

No objections. Is it much slower than our other CI tests?

[mxinden]

Running all quinn unit tests takes about 5 minutes, including dependency installation, build and emulator startup.

[larseggert]

Let's do a PR and see how long it takes.

Are there other targets we should be testing on?