dillon1000/react

[snap tester] Patch runner for sync mode

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`yarn snap --sync` currently fails on `error.file-has-non-critical-errors`. This 
is because we're relying on a globally overwritten `console.error` function to 
report non-fatal errors. However, executing `Promise.all(...)` on a single 
nodejs thread will interleave calls to `run` (which is an async function).