Bumps [mysql2](https://github.com/sidorares/node-mysql2) from 3.6.3 to 3.9.4.
- [Release notes](https://github.com/sidorares/node-mysql2/releases)
- [Changelog](https://github.com/sidorares/node-mysql2/blob/master/Changelog.md)
- [Commits](https://github.com/sidorares/node-mysql2/compare/v3.6.3...v3.9.4

)

---
updated-dependencies:
- dependency-name: mysql2
  dependency-type: direct:development
...

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: Chris Truter <chris@metabase.com>