Force local runs of devicelab tests to use en_US locale #54475
Description
Devicelab tests fail locally if the terminal locale isn't set to en_US (export LANG=en_US.UTF-8).
Updated instructions in https://github.com/flutter/flutter/wiki/Running-and-writing-tests#running-device-lab-tests-locally but it would be better if the tests handled forcing the locale.
See #51126 (comment).