Stop storing a reference in a lock guard

[yvt]

rust-lang/rust#97027

r3/src/r3_port_std/src/threading_windows.rs

Lines 234 to 237 in 57184ad

	pub struct MutexGuard<'a, T: ?Sized> {
	data: &'a mut T,
	locked: &'a AtomicBool,
	}

[yvt]

The fix is ready, but I'm not quite sure how to describe the motivations for the change.