Bump sp-staking from polkadot-v1.15.1 to polkadot-v1.16.0

Bumps [sp-staking](https://github.com/paritytech/polkadot-sdk) from polkadot-v1.15.1 to polkadot-v1.16.0.
- [Release notes](https://github.com/paritytech/polkadot-sdk/releases)
- [Changelog](https://github.com/paritytech/polkadot-sdk/blob/master/docs/RELEASE.md)
- [Commits](paritytech/polkadot-sdk@16b0fd0...87971b3)

---
updated-dependencies:
- dependency-name: sp-staking
  dependency-type: direct:production
...

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