Improve deposits migration

[aurexav]

Closes #1635.

[hackfisher]

@AurevoirXavier CI failed

[github-actions]

Check 6a6eaf9 crab-dev

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Check runtime storage

[github-actions]

Check 6a6eaf9 darwinia-dev

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[github-actions]

Check 6a6eaf9 koi-dev

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Pallet DarwiniaStaking
+ Entry: StorageEntryMetadata { name: "UnissuedReward", modifier: Default, ty: Plain(UntrackedSymbol { id: 6, marker: PhantomData<fn() -> core::any::TypeId> }), default: [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0], docs: [" Unissued reward to Treasury."] }

Pallet Deposit
+ Entry: StorageEntryMetadata { name: "MigrationFailures", modifier: Optional, ty: Map { hashers: [Blake2_128Concat], key: UntrackedSymbol { id: 0, marker: PhantomData<fn() -> core::any::TypeId> }, value: UntrackedSymbol { id: 368, marker: PhantomData<fn() -> core::any::TypeId> } }, default: [0], docs: [" Failures of migration.", "", " The first value is the deposits that failed to migrate,", " the second value is the type of failure."] }

[hackfisher]

Please bump spec version and release a new runtime for upgrade.

[hujw77]

LGTM