build(deps): bump once_cell from 1.5.2 to 1.6.0
Bumps [once_cell](https://github.com/matklad/once_cell) from 1.5.2 to 1.6.0.
- [Release notes](https://github.com/matklad/once_cell/releases)
- [Changelog](https://github.com/matklad/once_cell/blob/master/CHANGELOG.md)
- [Commits](https://github.com/matklad/once_cell/compare/v1.5.2...v1.6.0)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>
dependabot-preview[bot]