Manually disable normalized stress for MDS

Suppress a user warning from scikit-learn's MDS implementation caused by
not setting the `normalized_stress` value in v1.3. The default value changed
from `False` to `"auto"` in v1.4, but we want the original default
anyway so we set it here.

src/pathogen_embed/pathogen_embed.py

@@ -284,6 +284,7 @@ def embed(args):
             "n_jobs": 1,
             "n_init": 2,
             "random_state" : args.random_seed,
+            "normalized_stress": False,
         }
 
     # Override defaults with parameter values passed through embedding parameters, if