Update koa requirement from 2.6.1 to 2.6.2 (#3386)

Updates the requirements on [koa](https://github.com/koajs/koa) to permit the latest version.
- [Release notes](https://github.com/koajs/koa/releases)
- [Changelog](https://github.com/koajs/koa/blob/master/History.md)
- [Commits](https://github.com/koajs/koa/commits/2.6.2

)

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