test: add backup integration tests using snapshots #1004

Job	Run time
Cross checking x86_64-pc-windows-msvc	3m 37s
Cross checking x86_64-pc-windows-gnu	2m 39s
Cross checking x86_64-apple-darwin	4m 52s
Cross checking aarch64-apple-darwin	1m 10s
Cross checking x86_64-unknown-linux-gnu	3m 52s
Cross checking x86_64-unknown-linux-musl	43s
Cross checking aarch64-unknown-linux-gnu	4m 36s
Cross checking i686-unknown-linux-gnu	4m 38s
Cross checking x86_64-unknown-netbsd	3m 59s
Cross checking armv7-unknown-linux-gnueabihf	4m 35s
Cross checking x86_64-pc-windows-msvc	5m 5s
Cross checking x86_64-pc-windows-gnu	1m 27s
Cross checking x86_64-apple-darwin	5m 19s
Cross checking aarch64-apple-darwin	1m 8s
Cross checking x86_64-unknown-linux-gnu	29s
Cross checking x86_64-unknown-linux-musl	4m 11s
Cross checking aarch64-unknown-linux-gnu	4m 57s
Cross checking i686-unknown-linux-gnu	4m 47s
Cross checking x86_64-unknown-netbsd	5m 17s
Cross checking armv7-unknown-linux-gnueabihf	5m 0s
Result (Cross-CI)	1s
	1h 12m 22s

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