chore(test-react-app): refactor deprecated call to ReactDOM.render

[nickreynolds]

What issue is this PR fixing

• removes an error that can be safely ignored but can cause confusion

What is being changed

• just refactor how the root of the app is rendered

Quality

Check all that apply:

• I want these changes to be integrated
• I successfully ran pnpm i, pnpm build, pnpm test, pnpm test:browser locally.
• I allow my PR to be updated by the reviewers (to speed up the review process).
• I added unit tests.
• I added integration tests.
• I did not add automated tests because _________, and I am aware that a PR without tests will likely get rejected.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 89.72%. Comparing base (01de67d) to head (1a0a684).

Additional details and impacted files

@@           Coverage Diff           @@
##             next    #1418   +/-   ##
=======================================
  Coverage   89.72%   89.72%           
=======================================
  Files         177      177           
  Lines       26818    26818           
  Branches     2220     2220           
=======================================
  Hits        24062    24062           
  Misses       2756     2756           

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