WIP: flake-ify radicle-git #718

Job	Run time
build-macos	2m 50s
build-windows	5m 15s
cargo-deny (advisories)	27s
build-linux (stable)	1m 45s
cargo-deny (bans licenses sources)	29s
build-linux (nightly)	1m 49s
docs	1m 18s
fmt	27s
lint	1m 19s
test-linux (stable)	8m 10s
test-linux (nightly)	6m 34s
test-macos	4m 59s
	35m 22s

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