fix: check for isArray instead

[dmitrymatio]

Description

When only one child ({ }) is passed to children prop it can be either { } or [{ }] depending on how it was passed.
This is done for performance and consistent type reasons between rerenders. Changing the length check to isArray check to include this edge case.

Related Issue

Motivation and Context

How Has This Been Tested?

Screenshots (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• I have signed the Adobe Open Source CLA.
• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.

[dmitrymatio]

Fixes #1518. Missed tagging the issue sorry 🙏