fix: CancelSignaledChildWorkflow test

[roxblnfk]

Reason for This PR

React Promise v3 (cross dependency) has changed signature of the PromiseInterface::resolve() that requires a values as the first argument now.

Description of Changes

Fixed CancelSignaledChildWorkflow test.
Increased min PHP SDK version to 2.16.0 in composer.json

License Acceptance

By submitting this pull request, I confirm that my contribution is made under
the terms of the MIT license.

PR Checklist

[Author TODO: Meet these criteria.]
[Reviewer TODO: Verify that these criteria are met. Request changes if not]

• All commits in this PR are signed (git commit -s).
• The reason for this PR is clearly provided (issue no. or explanation).
• The description of changes is clear and encompassing.
• Any required documentation changes (code and docs) are included in this PR.
• Any user-facing changes are mentioned in CHANGELOG.md.
• All added/changed functionality is tested.