Zip/Verify benchmark doesn't work with `parallel` feature flag on

[frozenspider]

$ cargo bench --bench zip_benches --features "std parallel"
...
Benchmarking Zip/Verify: RandomField<4>, poly_size = 2^12(Int limbs = 1), ZipSpec1, modulus=106319353542452952636...: Warming up for 3.0000 s
thread 'main' panicked at benches/zip_benches.rs:216:22:
Failed to verify: InvalidPcsOpen("Proximity failure")