Extract a common_env_args bash array with the environment
variables shared by both unit and integration test containers
(BUILD_TARGET, RUSTFLAGS, TARGET_CC). The unit test block
uses common_env_args plus its own LLVM_PROFILE_FILE. After
the unit block, common_env_args is extended with the USER
and AUTH_DOWNLOAD_TOKEN variables used by all integration
test groups.
Assisted-by: GitHub Copilot:Claude-Opus-4.6
Signed-off-by: Muminul Islam <muislam@microsoft.com>