build(deps-dev): bump solidity-coverage from 0.7.16 to 0.7.21

Bumps [solidity-coverage](https://github.com/sc-forks/solidity-coverage) from 0.7.16 to 0.7.21.
- [Release notes](https://github.com/sc-forks/solidity-coverage/releases)
- [Changelog](https://github.com/sc-forks/solidity-coverage/blob/master/CHANGELOG.md)
- [Commits](https://github.com/sc-forks/solidity-coverage/commits)

---
updated-dependencies:
- dependency-name: solidity-coverage
  dependency-type: direct:development
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]