Maybe fix failing dependency?

services/ollama.nix

@@ -8,13 +8,18 @@
         services.open-webui.enable = true;
         services.open-webui.port = 8888;
 
-        #testing
         nixpkgs.overlays = [
             (final: prev: {
-                valkey = prev.valkey.overrideAttrs (oldAttrs: {
+                # We need to reach into the python package set
+                pythonPackagesExtensions = prev.pythonPackagesExtensions ++ [
+                    (python-final: python-prev: {
+                        langchain = python-prev.langchain.overridePythonAttrs (oldAttrs: {
+                            # This disables the checkPhase (running tests) for langchain
                             doCheck = false; 
                         });
                     })
                 ];
+            })
+        ];
     };
 }