Investigate flaky UI test case in storage_info_unsatisfied_nmap.rs

[KiChjang]

This UI test:

#[frame_support::pallet]
mod pallet {
	use frame_support::pallet_prelude::{Hooks, StorageNMap, Twox64Concat, NMapKey};
	use frame_system::pallet_prelude::BlockNumberFor;

	#[pallet::config]
	pub trait Config: frame_system::Config {}

	#[pallet::pallet]
	#[pallet::generate_storage_info]
	pub struct Pallet<T>(core::marker::PhantomData<T>);

	#[pallet::hooks]
	impl<T: Config> Hooks<BlockNumberFor<T>> for Pallet<T> {}

	#[pallet::call]
	impl<T: Config> Pallet<T> {}

	#[derive(codec::Encode, codec::Decode)]
	struct Bar;

	#[pallet::storage]
	type Foo<T> = StorageNMap<_, NMapKey<Twox64Concat, Bar>, u32>;
}

fn main() {
}

should yield the following error message:

error[E0277]: the trait bound `Bar: MaxEncodedLen` is not satisfied
  --> $DIR/storage_info_unsatisfied_nmap.rs:10:12
   |
10 |     #[pallet::generate_storage_info]
   |               ^^^^^^^^^^^^^^^^^^^^^ the trait `MaxEncodedLen` is not implemented for `Bar`
   |
   = note: required because of the requirements on the impl of `KeyGeneratorMaxEncodedLen` for `Key<frame_support::Twox64Concat, Bar>`
   = note: required because of the requirements on the impl of `StorageInfoTrait` for `frame_support::pallet_prelude::StorageNMap<_GeneratedPrefixForStorageFoo<T>, Key<frame_support::Twox64Concat, Bar>, u32>`
   = note: required by `storage_info`

However, the Key<Twox64Concat, Bar> syntax in the error message flip-flops between said form and NMapKey<Twox64Concat, Bar>. Further observations reveal that the test case was run twice, once with the --workspace parameter to cargo and the other without, suggesting that it may be related to cargo workspace issues. Other possible causes pin caching as the issue, however more investigation needs to be conducted to determine the root cause of the apparent non-determinism.

The aforementioned test case has been disabled by commenting out the test code in #8949 in order to not block the PR from landing.

[KiChjang]

cc @paritytech/ci