alpkit: Add tests for generated JSON schemas #57

Job	Run time
Run linters	34s
Test on x86_64-alpine-linux-musl (dynamically linked)	1m 41s
Test with --features shell-timeout	37s
Test with --features flate2-zlib --no-default-features	40s
Test with --features flate2-zlib-ng --no-default-features	41s
Test on x86_64-unknown-linux-musl with Rust stable	39s
Test on x86_64-unknown-linux-musl with Rust nightly	42s
Test on x86_64-unknown-linux-musl with Rust 1.65	3m 1s
Test on x86_64-unknown-linux-gnu with Rust stable	35s
Test on x86_64-apple-darwin with Rust stable	58s
Test on aarch64-unknown-linux-musl with Rust stable	3m 5s
Test on aarch64-unknown-linux-gnu with Rust stable	3m 19s
Test on armv7-unknown-linux-musleabihf with Rust stable	3m 21s
Test on powerpc64le-unknown-linux-gnu with Rust stable	3m 6s
Test on riscv64gc-unknown-linux-gnu with Rust stable	3m 0s
	25m 59s

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