Bump flat, eth-gas-reporter and solidity-coverage

Bumps [flat](https://github.com/hughsk/flat), [eth-gas-reporter](https://github.com/cgewecke/eth-gas-reporter) and [solidity-coverage](https://github.com/sc-forks/solidity-coverage). These dependencies needed to be updated together.

Updates `flat` from 4.1.1 to 5.0.2
- [Release notes](https://github.com/hughsk/flat/releases)
- [Commits](hughsk/flat@4.1.1...5.0.2)

Updates `eth-gas-reporter` from 0.2.25 to 0.2.27
- [Release notes](https://github.com/cgewecke/eth-gas-reporter/releases)
- [Changelog](https://github.com/cgewecke/eth-gas-reporter/blob/master/CHANGELOG.md)
- [Commits](https://github.com/cgewecke/eth-gas-reporter/commits/v0.2.27)

Updates `solidity-coverage` from 0.8.2 to 0.8.12
- [Release notes](https://github.com/sc-forks/solidity-coverage/releases)
- [Changelog](https://github.com/sc-forks/solidity-coverage/blob/master/CHANGELOG.md)
- [Commits](sc-forks/solidity-coverage@v0.8.2...v0.8.12)

---
updated-dependencies:
- dependency-name: flat
  dependency-type: indirect
- dependency-name: eth-gas-reporter
  dependency-type: indirect
- dependency-name: solidity-coverage
  dependency-type: indirect
...

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