Add "safe_serialization": true as is required for custom Nomic models

Hello!

As discussed, this adds safe_serialization=True when loading the model. I haven't tested this personally, but I have a strong suspicion that it should work, based on [this](https://huggingface.co/nomic-ai/nomic-embed-text-v1.5/blob/main/sentence_bert_config.json#L5).

- Tom Aarsen

sentence_bert_config.json

@@ -2,6 +2,7 @@
   "max_seq_length": 8192,
   "do_lower_case": false,
   "model_args": {
-    "add_pooling_layer": false
+    "add_pooling_layer": false,
+    "safe_serialization": true
   }
 }