chore(deps): Update Rust crate nix to 0.31 #300

Job	Run time
Minimal versions (ubuntu-latest)	24s
Test (ubuntu-latest, stable)	29s
Docs	24s
Check MSRV (ubuntu-latest)	28s
lockfile	14s
Coverage	37s
rustfmt	19s
clippy	31s
CI	4s
	3m 30s

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