Unable to properly benchmark pallet_bounties when ED is 0

[tsenovilla]

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Description of bug

We cannot properly benchmark pallet_bounties in the LAOS runtime, as all the following benchmarks fail:

The following 7 benchmarks failed:
- pallet_bounties::accept_curator
- pallet_bounties::award_bounty
- pallet_bounties::claim_bounty
- pallet_bounties::close_bounty_active
- pallet_bounties::extend_bounty_expiry
- pallet_bounties::propose_curator
- pallet_bounties::unassign_curator
Error: Input("7 benchmarks failed")

Upon investigation, we believe this issue may affect all runtimes where the existential deposit is set to 0, as is our case. This issue in LAOS outlines the root cause of this behavior, but I’ve included the relevant details below for easier tracking.

Concretely, this function is used in benchmarks to fund the treasury account.
If ED is 0, so is T::Currency::minimum_balance(), resulting in the treasury's balance being initialized to 0 before benchmarks that require treasury funding.

As a result, there is no budget available for bounties in the benchmark suite. Consequently, these lines remain unreachable, preventing bounties from getting the Funded status. While not all the failing benchmarks depend directly on the Funded status, they do rely on a flow where the bounty has successfully progressed through that stage, hence the failure.

Steps to reproduce

Set a runtime using pallet_treasury + pallet_bounties as SpendFunds where the existential deposit is 0 and try to benchmark pallet_bounties. LAOS is affected by this issue, so it may be used as reference as well

[AurevoirXavier]

Generally, I write this code for such issues. (a lot of pallets had such issues in the past)

#[cfg(feature = "runtime-benchmarks")]
const ED = 1;
#[cfg(not(feature = "runtime-benchmarks"))]
const ED = 0;

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But it's okay to report such issues and see if we can improve the benchmarks.