build(deps): bump the amplify group across 1 directory with 2 updates

Bumps the amplify group with 2 updates in the /frontend directory: [@aws-amplify/auth](https://github.com/aws-amplify/amplify-js) and [aws-amplify](https://github.com/aws-amplify/amplify-js).


Updates `@aws-amplify/auth` from 5.6.12 to 6.3.8
- [Release notes](https://github.com/aws-amplify/amplify-js/releases)
- [Commits](https://github.com/aws-amplify/amplify-js/compare/@aws-amplify/[email protected]...@aws-amplify/[email protected])

Updates `aws-amplify` from 5.3.19 to 6.4.0
- [Release notes](https://github.com/aws-amplify/amplify-js/releases)
- [Commits](https://github.com/aws-amplify/amplify-js/compare/[email protected]@6.4.0)

---
updated-dependencies:
- dependency-name: "@aws-amplify/auth"
  dependency-type: direct:production
  update-type: version-update:semver-major
  dependency-group: amplify
- dependency-name: aws-amplify
  dependency-type: direct:production
  update-type: version-update:semver-major
  dependency-group: amplify
...

Signed-off-by: dependabot[bot] <[email protected]>