Bump hashicorp/aws from 6.15.0 to 6.21.0 in /examples/basic_usage

Bumps [hashicorp/aws](https://github.com/hashicorp/terraform-provider-aws) from 6.15.0 to 6.21.0.
- [Release notes](https://github.com/hashicorp/terraform-provider-aws/releases)
- [Changelog](https://github.com/hashicorp/terraform-provider-aws/blob/main/CHANGELOG.md)
- [Commits](hashicorp/terraform-provider-aws@v6.15.0...v6.21.0)

---
updated-dependencies:
- dependency-name: hashicorp/aws
  dependency-version: 6.21.0
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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Author: dependabot[bot]