ErrorBoundary.fallbackUI can't be a node

[ijsnow]

Description of the change

The ErrorBoundary component's propTypes field says that it can be a react node or a function. However, if passed a node (e.g. <p>oops</p>), you get the following error:

Element type is invalid: expected a string (for built-in components) or a class/function (for composite components) but got: object.

Check the render method of `ErrorBoundary`.

This PR simply removes the PropTypes.node reference from the definition.

Type of change

• Bug fix (non-breaking change that fixes an issue)

Checklists

Development

• Lint rules pass locally
• All tests related to the changed code pass in development

Code review

• This pull request has a descriptive title and information useful to a reviewer. There may be a screenshot or screencast attached
• "Ready for review" label attached to the PR and reviewers assigned
• Changes have been reviewed by at least one other engineer

[waltjones]

Good catch!

This also helped me find and fix a couple other test/CI related issues.
#49
#50