Fix React PropTypes warning in tests for Immutable plugin

[pedrottimark]

Summary

After changes for upgrade to Flow 0.53.1, immutable.test.js had 2 occurrences of:

console.warn node_modules/react/lib/lowPriorityWarning.js:40
Warning: Accessing PropTypes via the main React package is deprecated, and will be removed in React v16.0. Use the latest available v15.* prop-types package from npm instead. For info on usage, compatibility, migration and more, see https://fb.me/prop-types-docs

After reading https://flow.org/en/docs/react/types/

If you want to access them [utility types] then you should import React as a namespace import * as React from 'react'

if you import React with: import React from 'react' you will be able to access React.createElement()

These tests depend only on React.createElement() not on any utility types.

Test plan

Check console in CI

[github-actions]

This pull request has been automatically locked since there has not been any recent activity after it was closed. Please open a new issue for related bugs.
Please note this issue tracker is not a help forum. We recommend using StackOverflow or our discord channel for questions.