chore: bump @aws-sdk/karma-credential-loader from 3.13.0 to 3.21.0

Bumps [@aws-sdk/karma-credential-loader](https://github.com/aws/aws-sdk-js-v3/tree/HEAD/packages/karma-credential-loader) from 3.13.0 to 3.21.0.
- [Release notes](https://github.com/aws/aws-sdk-js-v3/releases)
- [Changelog](https://github.com/aws/aws-sdk-js-v3/blob/main/packages/karma-credential-loader/CHANGELOG.md)
- [Commits](https://github.com/aws/aws-sdk-js-v3/commits/v3.21.0/packages/karma-credential-loader)

---
updated-dependencies:
- dependency-name: "@aws-sdk/karma-credential-loader"
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

Author: dependabot[bot]