fix: update LDProvider mock to match implementation signature

[jamiehaywood]

Requirements

• [x] I have added test coverage for new or changed functionality
• [x] I have followed the repository's pull request submission guidelines
• [x] I have validated my changes against all supported platform versions

Related issues

closes #31

Describe the solution you've provided

Updated the mockImplementation signature to avoid Objects are not valid as a React child (found: object with keys {clientSideID, options, children}) error during testing

Describe alternatives you've considered

N/A

Additional context

Add any other context about the pull request here.

[jamiehaywood]

awesome thanks v. much @yusinto - thanks for your quick turnaround :)