⬇️(backend) downgrade langfuse to version 3.11.2

We to keep in sync the version of the sdk client and the version of the
langfuse server. For now we can't upgrade langfuse See
https://github.com/langfuse/langfuse/issues/11564

renovate.json

@@ -43,6 +43,12 @@
       "matchPackageNames": ["pydantic-ai-slim"],
       "allowedVersions": "<1.59.0"
     },
+    {
+      "groupName": "allowed langfuse versions",
+      "matchManagers": ["pep621"],
+      "matchPackageNames": ["langfuse"],
+      "allowedVersions": "<3.12.0"
+    },
     {
       "enabled": false,
       "groupName": "ignored js dependencies",

src/backend/pyproject.toml

@@ -48,7 +48,7 @@ dependencies = [
     "factory_boy==3.3.3",
     "gunicorn==25.1.0",
     "jsonschema==4.26.0",
-    "langfuse==3.14.5",
+    "langfuse==3.11.2",
     "lxml==6.0.2",
     "markdown==3.10.2",
     "mozilla-django-oidc==5.0.2",