test(ffe): cover billed source precedence

tests/parametric/test_dynamic_configuration.py

@@ -41,6 +41,8 @@
     # Decrease the heartbeat/poll intervals to speed up the tests
     "DD_TELEMETRY_HEARTBEAT_INTERVAL": "0.2",
     "DD_REMOTE_CONFIG_POLL_INTERVAL_SECONDS": "0.2",
+    # This suite validates RC capabilities; Feature Flagging RC is explicit opt-in.
+    "DD_FEATURE_FLAGS_CONFIGURATION_SOURCE": "remote_config",
     # Disable CSS which is enabled by default on Go
     "DD_TRACE_STATS_COMPUTATION_ENABLED": "false",
 }