Fix UB in destroy_array test

[taiki-e]

Reportrd by Miri in #578 (log)

crossbeam/crossbeam-epoch/src/collector.rs

Lines 378 to 388 in e08b21c

	let mut v = Vec::with_capacity(COUNT);
	for i in 0..COUNT {
	v.push(i as i32);
	}
	let ptr = v.as_mut_ptr() as usize;
	let len = v.len();
	guard.defer_unchecked(move || {
	drop(Vec::from_raw_parts(ptr as *const u8 as *mut u8, len, len));
	DESTROYS.fetch_add(len, Ordering::Relaxed);
	});

ptr is a pointer to Vec<i32>, but deallocated as Vec<u8>.

[jeehoonkang]

bors r+

[bors]

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