Bump aws-sigv4 from 1.2.1 to 1.5.1

Bumps [aws-sigv4](https://github.com/aws/aws-sdk-ruby) from 1.2.1 to 1.5.1.
- [Release notes](https://github.com/aws/aws-sdk-ruby/releases)
- [Changelog](https://github.com/aws/aws-sdk-ruby/blob/version-3/gems/aws-sigv4/CHANGELOG.md)
- [Commits](https://github.com/aws/aws-sdk-ruby/compare/1.2.1...1.5.1

)

---
updated-dependencies:
- dependency-name: aws-sigv4
  dependency-type: indirect
  update-type: version-update:semver-minor
...

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