test

Bump proptest from 1.5.0 to 1.6.0 #326

Job	Run time
Run the big ignored tests	1m 7s
Build & test (ubuntu-latest, stable)	36s
Build & test (ubuntu-latest, beta)	39s
Build & test (ubuntu-latest, nightly)	41s
Clippy lints	16s
32bit tests	33s
Build & test (macos-latest, stable)	40s
Check documentation links	6s
Check formatting	4s
Build & test (macos-latest, beta)	50s
Build & test (macos-latest, nightly)	41s
Check it compiles on old Rust (1.31.0)	1m 16s
Build & test (windows-latest, stable)	2m 59s
Build & test (windows-latest, beta)	2m 29s
Verify benchmarks compile	51s
Build & test (windows-latest, nightly)	2m 57s
Test with experimental-thread-local	44s
Miri checks	9m 1s
Check it compiles on old Rust (1.45.0)	9s
Thread Sanitizer checks MacOS	15s
	26m 54s

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