### What does this PR do?
Adds a max-concurrency flag to limit the amount of concurrent tests that
run at once. Defaults to 20. Jest and Vitest both default to 5.
### How did you verify your code works?
Tests
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Co-authored-by: coderabbitai[bot] <136622811+coderabbitai[bot]@users.noreply.github.com>
Co-authored-by: Jarred Sumner <jarred@jarredsumner.com>