build(deps-dev): bump @aws-cdk/cx-api from 2.19.0 to 2.20.0 (#738)

Bumps [@aws-cdk/cx-api](https://github.com/aws/aws-cdk/tree/HEAD/packages/@aws-cdk/cx-api) from 2.19.0 to 2.20.0.
- [Release notes](https://github.com/aws/aws-cdk/releases)
- [Changelog](https://github.com/aws/aws-cdk/blob/master/allowed-breaking-changes.txt)
- [Commits](https://github.com/aws/aws-cdk/commits/HEAD/packages/@aws-cdk/cx-api)

---
updated-dependencies:
- dependency-name: "@aws-cdk/cx-api"
  dependency-type: direct:development
  update-type: version-update:semver-minor
...

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Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]