test: speedup process-title-threadsafe on macOS
test: speedup process-title-threadsafe on macOS

This test has been timing out on macOS. Try to avoid that by
reducing the number of iterations run.

PR-URL: https://github.com/libuv/libuv/pull/1867
Reviewed-By: Santiago Gimeno <3f17e29e343c4cf8809fb0970d81d6d8ee88d6b3@gmail.com>
Reviewed-By: Bert Belder <9f2ff180696da386c1be31b4507155616db25dc6@gmail.com>

unknownbrackets/maxcso,unknownbrackets/maxcso,unknownbrackets/maxcso,unknownbrackets/maxcso,unknownbrackets/maxcso,unknownbrackets/maxcso,unknownbrackets/maxcso