alpkit: Add tests for generated JSON schemas #58

Job	Run time
Test on x86_64-alpine-linux-musl (dynamically linked)	1m 33s
Test with --features shell-timeout	39s
Test with --features flate2-zlib --no-default-features	46s
Test with --features flate2-zlib-ng --no-default-features	1m 0s
Run linters	30s
Test on x86_64-unknown-linux-musl with Rust stable	53s
Test on x86_64-unknown-linux-musl with Rust nightly	43s
Test on x86_64-unknown-linux-musl with Rust 1.65	4m 14s
Test on x86_64-unknown-linux-gnu with Rust stable	54s
Test on x86_64-apple-darwin with Rust stable	1m 30s
Test on aarch64-unknown-linux-musl with Rust stable	3m 45s
Test on aarch64-unknown-linux-gnu with Rust stable	3m 0s
Test on armv7-unknown-linux-musleabihf with Rust stable	3m 21s
Test on powerpc64le-unknown-linux-gnu with Rust stable	3m 27s
Test on riscv64gc-unknown-linux-gnu with Rust stable	1m 17s
	27m 32s

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