[pallet_collective] Benchmark fails with MaxProposals greater 255

[Chralt98]

Hey valuable Substrate maintainers,

the current benchmark of pallet_collective fails on propose_proposed with DuplicateProposal, when the MaxProposals number is set greater than u8::MAX. This happens because the proposal hash inside the benchmark is generated based on the MaxProposals number and produces duplicated (non-unique) hashes after the number of 255 is reached.

substrate/frame/collective/src/benchmarking.rs

Line 199 in 174735e

let proposal: T::Proposal = SystemCall::<T>::remark { remark: vec![p as u8; b as usize] }.into();

The ProposalIndex is not u8 to allow more than 255 proposals.