ci(langchain): re-enable latest langchain tests with cassettes (#6243)

* tracing plugin tests

* llmobs tests, plus some fixups to apm tracing tests

* cassettes

* use testagent 1.31.1

* small tweak

Author: sabrenner

docker-compose.yml

@@ -177,7 +177,7 @@ services:
       - LDAP_PASSWORDS=password1,password2
 
   testagent:
-    image: ghcr.io/datadog/dd-apm-test-agent/ddapm-test-agent:v1.27.4
+    image: ghcr.io/datadog/dd-apm-test-agent/ddapm-test-agent:v1.31.1
     ports:
       - "127.0.0.1:9126:9126"
     environment: