Update Rust crate proptest to 1.6.0 #1411

Job	Run time
Lint	1m 13s
Cross-compile to aarch64	1m 30s
Build and test core crates (ubuntu-latest, 1.78)	1m 57s
Build and test core crates (ubuntu-latest, stable)	1m 58s
Build and test (all features) (ubuntu-latest, 1.78)	3m 10s
Build documentation (ubuntu-latest)	55s
Build and test core crates (macos-14, 1.78)	1m 49s
Build and test (all features) (ubuntu-latest, stable)	2m 50s
Build and test core crates (macos-14, stable)	1m 41s
Build and test (all features) (macos-14, 1.78)	2m 33s
Build and test core crates (windows-latest, 1.78)	5m 3s
cargo-compare extended tests (ubuntu-latest)	2m 58s
Build and test (all features) (macos-14, stable)	3m 20s
cargo-compare extended tests (macos-14)	2m 32s
Build and test (all features) (windows-latest, 1.78)	6m 29s
Build and test core crates (windows-latest, stable)	6m 18s
Build and test (all features) (windows-latest, stable)	6m 58s
	53m 14s

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