Add single child and array with one item key equality test to address TODO comment

[D-Elbel]

Summary

Added a test to address old TODO comment within ReactChildren.

How did you test this change?

Ran React Children test suite.

[react-sizebot]

Comparing: 746890329452cbec8685eb3466847c5f17d9dc77...8a3d35a4b72ebe6815e75c0edbb31876399da272

Critical size changes

Includes critical production bundles, as well as any change greater than 2%:

Name	+/-	Base	Current	+/- gzip	Base gzip	Current gzip
oss-stable/react-dom/cjs/react-dom.production.min.js	=	175.90 kB	175.90 kB	=	54.76 kB	54.76 kB
oss-experimental/react-dom/cjs/react-dom.production.min.js	=	177.97 kB	177.97 kB	=	55.40 kB	55.39 kB
facebook-www/ReactDOM-prod.classic.js	=	569.66 kB	569.66 kB	=	100.26 kB	100.26 kB
facebook-www/ReactDOM-prod.modern.js	=	553.51 kB	553.51 kB	=	97.35 kB	97.35 kB

Significant size changes

Includes any change greater than 0.2%:

(No significant changes)

Generated by :no_entry_sign: dangerJS against 8a3d35a4b72ebe6815e75c0edbb31876399da272

[github-actions[bot]]

This pull request has been automatically marked as stale. If this pull request is still relevant, please leave any comment (for example, "bump"), and we'll keep it open. We are sorry that we haven't been able to prioritize reviewing it yet. Your contribution is very much appreciated.

[github-actions[bot]]

Closing this pull request after a prolonged period of inactivity. If this issue is still present in the latest release, please ask for this pull request to be reopened. Thank you!