Enable PHP FFE evaluation metric system tests (#7033)

Author: leoromanovsky

manifests/php.yml

@@ -607,7 +607,7 @@ manifest:
   tests/docker_ssi/test_docker_ssi_crash.py::TestDockerSSICrash::test_crash: missing_feature (No implemented the endpoint /crashme)
   tests/ffe/test_dynamic_evaluation.py: v1.21.0-dev
   tests/ffe/test_exposures.py: v1.21.0-dev
-  tests/ffe/test_flag_eval_metrics.py: missing_feature
+  tests/ffe/test_flag_eval_metrics.py: v1.21.0-dev
   tests/integration_frameworks/llm/anthropic/test_anthropic_llmobs.py::TestAnthropicLlmObsMessages::test_create_error: bug (MLOB-1234)
   tests/integrations/crossed_integrations/test_kafka.py::Test_Kafka: missing_feature
   tests/integrations/crossed_integrations/test_kinesis.py::Test_Kinesis_PROPAGATION_VIA_MESSAGE_ATTRIBUTES: missing_feature