[ci] don't mutate BUILD_ENVIRONMENT in test.sh (#80144)
We append TEST_CONFIG to BUILD_ENVIRONMENT at the beginning of test.sh
This is bad because it alters a fundamental env var, and also isn't
really necessary because it doesn't add information.
In most case where we check BUILD_ENV, we also check TEST_CONFIG, making
it redundant anyway.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/80144
Approved by: https://github.com/malfet, https://github.com/janeyx99
