test(maitake-sync): test that futures are `!Unpin` #1342

Job	Run time
changed_paths	6s
clippy	3m 3s
build boot image (x86_64)	3m 30s
Loom tests (cordyceps)	1m 47s
cargo check (host)	3m 52s
Miri tests (codyceps)	2m 21s
docs	4m 21s
Loom tests (maitake)	4m 34s
Tests (maitake, no-default-features)	1m 42s
rustfmt	22s
cargo test (host)	4m 45s
cargo test (cross x64)	4m 13s
Loom tests (mycelium-util)	1m 9s
	35m 45s

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