Remove an unused import from the timeout env var test

The EnvironmentVariables symbol is reached through the env_module alias,
so the direct import was dead and tripped ruff F401/I001 in CI.

Author: chakrris

tests/lib/test_client_timeout_env.py

@@ -18,7 +18,6 @@
     _timeout_from_env,
     create_async_agentex_client,
 )
-from agentex.lib.environment_variables import EnvironmentVariables
 
 
 @pytest.fixture(autouse=True)